Pentagrams were used symbolically in ancient Greece and Babylonia. The pentagram has magical associations, and many people who practice Neopagan faiths wear jewelry incorporating the symbol. Christians once more commonly used the pentagram to represent the five wounds of Jesus, and it also has associations within Freemasonry.

The pentagram has long been associated with the planet Venus, and the worship of the goddess Venus, or her equivalent. It is also associated with the Roman Lucifer, who was Venus as the Morning Star, the bringer of light and knowledge. It is most likely to have originated from the observations of prehistoric astronomers. When viewed from Earth, successive inferior conjunctions of Venus plot a nearly perfect pentagram shape around the zodiac every eight years.

NOT SATANIC. So all you "blaaaargh i haf 666 and pentagram on my shirt i luv devil" are doing it wrong.