The trident is the attribute of many terrific deities and of the oracles who during the trances are holding the weapons of the deities by whom they are possessed.

Often, as in this case, a skull is situated at the base of the big central blade, while two smaller blades are on the left and on the right of it.  Flames are coming up from the centre of the blades.  Blades and flames have the purpose of destroying all malefic sources and influences.