Satanism

A goat's head inscribed in a downward-pointing pentagram, from La Clef de la Magie Noire by the Rosicrucian Stanislas de Guaita (1897).

Satanists use a pentagram with two points up, often inscribed in a double circle, with the head of a goat inside the pentagram.

This is referred to as the Sigil of Baphomet.

They use it much the same way as the Pythagoreans, as Tartaros literally translates from Greek as a "Pit" or "Void" in Christian terminology (the word is used as such in the Bible, referring to the place where the fallen angels are fettered).

The Pythagorean Greek letters are most often replaced by the Hebrew letters לויתן forming the name Leviathan.

Less esoteric LaVeyan Satanists use it as a sign of rebellion or religious identification, the three downward points symbolising rejection of the holy Trinity.