It indicates the Jaffa's rank. Your basic Jaffa soldier will have the symbol of his System Lord tattooed to his forehead in black ink. The First Prime (or ex-First Prime, for that matter) however, has a golden symbol instead to make him or her stand out from a group of regular Jaffa. Silver marks appear to indicate status of a Jaffa who is neither a First Prime nor a regular soldier.
The golden symbol is created by cutting the skin and pouring molten gold into the wouldwound.
