Pentagrams ... 
I am not exactly aware how does the Pentagram acts as an effective talisman over negative forces but they do.
My Research on that is still on.
The five-pointed star, or pentagram is one of the most potent, powerful, and persistent symbols in human history. It has been important to almost every ancient culture, from the Mayans of Latin America, to India, China, Greece, and Egypt. It has been found scratched on the walls of Neolithic caves, and in Babylonian drawings, where it marks the pattern the planet Venus makes on its travels- a secret symbol of the Goddess Ishtar. Scriptures, especially Hebrew, are abundant with references to pentagrams. So, why does this symbol have such a sinister reputation today?
The Pentagram in the Ancient World
The earliest pentagrams were rough diagrams found scratched into stone age caves. While they are believed to have some spiritual significance, the meaning of the star-shape to early humans is a mystery. In the civilizations that followed, it held various meanings, usually astronomical and religious. Pentagrams served to mark directions in Sumerian texts, and represented the five visible planets. Later, it was the sign of the planet Venus and the goddess .
According to the Greek mathematician and philosopher Pythagoras, five was the number of man, because of the fivefold division of the body, and the ancient Greek division of the soul. According to Pythagoras, the five points of the pentagram each represent one of the five elements that make up man: fire, water, air, earth, and psyche. (energy, fluid, breath, matter, and mind; liquid, gas, solid, plasma and aethyr) The Pythagoreans held the pentacle sacred to Hygeia, the Goddess of healing, whose name (HGIEiA) was an anagram in Greek for the elements water, earth, spirit, fire, and air.
This particular symbolism has persisted for centuries, and has greatly influenced theologies of diverse traditions. Early Christians wore it as an emblem, possibly to represent the wounds of Christ, or possibly due to connections between early Christians and the Pythagorean mysteries.* Later, the pentacle was important to many doctrines of esoteric Medieval and Renaissance belief systems- alchemy, kabbalah, and Ceremonial magick.
Possibly before ancient Sumerian astronomers observed the curious natural phenomena that of the seven visible planets, only Venus traced a regular geometric pattern, a pentagram in eight-year cycles, this number and figure may have already achieved symbolic import. We can confirm at least that what was observed above, was repeated by man here below. In examining remaining monuments of this distant past we find evidence that in fact the symmetry of the pentagram was utilized in mans most important architectural edifices. We may also interpret the stone work of this initiatic tradition in light of literary references to such western traditions such as those of the Pythagoreans, Jews, Christians, Druids, as well as the Lataif of Sufi tradition, and Hindu Tattwas. The pentagram served the Pythagoreans as a salutation and a symbol of health. Medieval masons considered it a symbol of deep wisdom and integrated its proportions in ecclesiastical edifices. In recent times, professor Matila Gyrka called the pentagram the "gateway to absolute independence;" "symbol of deep wisdom;" and an "ideal archetype of dynamic growth."
The Pentacle and Magick
Ritual magicians, like the Greeks, used the Pentagram as a microcosm of the human body. The practice of Ritual Magick was used to create a state of closeness with god through the use of symbols and rituals to imitate the divine state. It was believed that like affects like, that the connection between the world of symbols and the world of actions could also be manipulated for evil purposes. One of these magicians, Giordano Bruno , warned of such misuse of the powerful pentacle by Black magicians. (The pentagram is still central to the practice of ritual magick, and is used in the foundation of many of its rituals.)
In the Jewish kabbalistic tradition, which borrows many Pythagorean ideas, the pentagram represents the five upper sephiroth on the Tree of Life- five numbers, being indivisible by any but themselves, which represent pure archetypal forces: justice, mercy, wisdom, understanding, and transcendent splendor.
There are many connections between the pentagram and and other religions. It was a preferred emblem to adorn the jewelry and amulets of early Christians (followed by an 'x' or a phoenix). The pentagram was associated with the five wounds of Christ, and because it could be drawn in one continuous movement of the pen, the Alpha and the Omega as one. It was also an expression of a secret Gnostic heresy, found hidden here and there throughout Christian history- a symbol of Isis/Venus as the secret goddess, the female principle. The most notable instance of this symbolism is in the Arthurian Grail romances, which are Gnostic and kabbalistic teachings disguised as tales of knightly quests. 
The pentacle as a symbol of the feminine principle was was embodied by the rose. The small, five petalled roses found in many gothic cathedral ornamentation are not-so-secret pentagrams.
The Pentacle in Wicca and other Neopagan Traditions
Currently, the most common religious uses of the pentagram are by Wiccan, Neopagan, and Satanic groups. In most Wiccan and Neopagan traditions, its symbolic meaning is derived from Ceremonial magick and nineteenth century occultism- the four elements ruled by the spirit- although as these theologies mature, they have added to its meaning. In many of these traditions, it can also symbolize the unity of mankind with the earth or with the realm of the spirit, the human body, and more.
Point up, or Point Down?
A "point down" pentacle is nothing new- nor is it necessarily Satanic when it appears as such. Historical depictions of the pentagram were as likely to be points down as point up- a distinction between one or the other was rarely made by the ancients. Even today, one must not assume a point down pentagram is Satanic, as it is just likely to be Masonic, Wiccan, or simply upside-down. Some inexperienced Wiccans will occasionally claim that a point down pentacle is Satanic, but such a symbol has at times represented the Wiccan horned God, and is still today an emblem of the Second Degree initiation in Gardnerian Wicca.
The Satanic Pentagram
In the minds of many , the pentagram is inextricably linked with black magick and Satan worship. The Satanic pentagram is a difficult symbol- it is the newest and least used, but at the same time the best known and most controversial. The Satanic pentacle is almost always presented upside down, or inverted, with a single point facing downward, and it is this pentacle that is presented incorrectly as 'evil.'
The adoption of the pentacle as a Satanic emblem is quite recent, dating only to the latter half of the twentieth century. To the Satanist, this glyph is a representation of "Black magic," symbolizing the triumph of matter and individual desires over religious dogma- earth over an illusory promise of heaven. It is not analogous to the upturned cross (which is a symbol of rebellion against Christian culture), and is not "anti-Wiccan."
In modern Satanic theology, the pentagram is far more likely to represent the individual, or the choice to pursue individual glory or immortality rather than union or absorption with the divine- where some traditions advocate the sublimation of the ego or submission to god, Satanism exalts and glorifies it, deifying the human being. The symbol most commonly associated with Satanic practices is the "Sabbatic goat" or Goat of Mendes pentacle, often confused with Baphomet, a figure from Templar legend, and Pan, the Greek goat God. It rarely has any deeper meaning; an irony when one considers that its association with Satanism has made the pentagram a feared symbol to many, and the subject of countless conspiracy theories.The Goat's Head :
The goat itself is related to medieval superstitions about the behavior of witches, who were often depicted dancing with or riding on goats (who often represented Satan himself). The goat in that context is often seen as an ironic symbol of sexual repression (the association being a clear allusion to the unrestrained sexuality represented by this ancient fertility symbol), so one can see why the symbolism might appeal to modern Satanists, as a symbol of freedom from sexual and religious taboos.
The Pentagram in Freemasonry
In Freemasonry and related traditions, the pentagram is usually referred to as the "blazing star," and in addition to more traditional Pythagorian symbolism, is sometimes symbolic of the descent of the divinity of Christ into the world of matter, a remnant of Masonry's ties with medieval Christian Kabbalah and hermeticv tradition. In this, it represents the Star of Bethlehem. Freemasonry emphasizes Pythagorean geometry in its system of allegorical symbology, and as the pentagram was the chief of the Pythagorean symbols, it is not at all surprising to find it among Masonic symbols. Even so, it is still a relatively minor symbol in freemasonry, and largely ignored in today's lodges. 
The Masonic use of the pentagram has nevertheless provided endless fodder for conspiracy minded evangelicals who see its use as proof of a vast Satanic Masonic network. Many absurd connections have been made between the Satanic pentagram and the Masonic star by enthusiastic conspiracy theorists, who fail to note that the first association of the reversed pentacle with 'evil' is a relatively recent attitude- adopted long after Masons had been using the star without controversy for a very long time. The 19th century magical scholar Eliphas Levi is the first known to have vested the downward pointing pentacle with any real negative meaning, elaborating perhaps on Bruno's earlier claims. It was not until the mid twentieth century that Levi's 'Mendes' pentacle was adopted as an emblem of modern Satanism. No Satanic or black magic group is known to have used a pentagram before then, and even the oldest representations of black masses and other 'satanic' activities contain no pentagrams.
The Pentagram of the Founders
Surprisingly, the pentagram also plays an important part in the symbology of the early United States government (a fact not lost on the conspiracy theorists, of course.). Many of the Founding Fathers were Freemasons, to whom the Pentagram is an important symbol (see above). The five pointed star appears in much of our early iconography- the US flag, the Great Seal, and on our currency. It is even to be found in the Capitol, where the White House sits at the apex of a giant pentagram, one of many interesting features in Capitol geometry:
Map of Washington
Pentagram in nature:
The pentagram was also associated with the golden ratio (which it includes), and the dodecahedron, the fifth Platonic solid, which has twelve pentagonal faces and was considered by Plato to be a symbol of the heavens. Burkert says that the pentagram had a secret significance and power to the pythagoreans, and was used as a password or symbol of recognition amongst themselves.
The Golden ration: 0.618 : 1 : 1.618
Compiled by Sudip K Ghosh aka *~Anecentric