A sigil is a magical symbol, a symbol believed to hold connections to a greater supernatural power. Sigils are often related to Religion.
There are three main forms of modern religion Satanism -- One is an atheistic religion founded by Anton Lavey, and is also referred to as Atheistic Satanism or LaVeyan Satanism. They do not believe in Satan but see him as a metaphor for qualities the majority wish to oppress. The second kind is Temple Satanism, founded by Lucien Greaves forming the Satanic Temple in 2013. It is a more politically active organization, and without any of the magical practices of LeVeyan Satanism. The third kind is Theistic Satanism, also known as Spiritual Satanism, in which people believe in and worship Satan as a god. This symbol dates back to the 1400s, but has always been associated with Lucifer. According to contemporary Christianity, Lucifer was a fallen angel of God who was cast down from heaven for challenging God, both in power and challenging God's views of the expecting worship. Lucifer took pride in his power, which was the 7th and deadliest of all the sins, and when questioning God, was damned for eternity in Hell. This version of the story is an interpretation of an allegory found in Isaiah 14:12-15.
The first appearance of this sigil was in Italy, while it was still many city-state tribes of Italy that spawned from the Latin-speaking Roman Empire, before they unified back into the country of Italy in the 1800s. This sigil appeared in a book called the Grimoirium Verum, which means the "Grimoire of Truth"
Lucifer and Satan have long been conflated, along with the Devil and the figure of Baphomet, a winged androgyny with the head of a goat. The Church of Satan uses the "Sigil of Baphomet" as part of its visual iconography.