A symbol for the alchemical element Sulfur, (Brimstone) which is spiritually analogous to the human soul. Alchemically, sulfur has the qualities of masculine, hot and dry. Combined with Mercury (feminine, cool and moist), the pair were considered the parents of all metals.
Alchemical drawings often portray Sulfur as the sun. (In some views, sulfur and salt are the parents of Mercury) The symbol of sulfur is often used as an identifying symbol by Satanists, due to sulphur’s historical asociation with the devil.
This glyph is often referred to incorrectly as the “pontifical cross of Satan” by Christian tract writers, due to its adoption as an emblem of Satanism by Anton LaVey in the 1960s. The emblem has no history as a symbol of Satanism outside of LaVey’s usage, and the attribution is most likely a product of anti-Catholic sentiment, as it is often compared in this context to the Catholic Pontifical Cross. A more common symbol for sulfur is a fire triangle surmounting a cross of earth: