The pentagram and The Sigil of The Baphomet
The pentagram has been a symbol of the occult for more than five
millenia, but the left hand path has taken to the "two points up,
one down" version as their symbol. If you add a goats head inside
the pentagram and the ancient hebrew (caballic) symbols of the five
forces of nature (earth, air, fire, water, mind/spirit) which also
happens to be the letters making up the name 'Leviathan' in a
circle surrounding it, you get The Sigil of The Baphomet, the
official 'logo' of The Church of Satan.
They didn't invent this or own it; its design came from Eliphas
Levi in 1855, but probably originate from the Knights Templar,
possibly among the earliest european left hand path practitioners
in the middle ages (early 1300's). You can read more about the
Baphomet and its history below.
