So I concluded he was carrying something that the necromancer gave him.
A charm sounds odd for necromancer magic. But talisman and amulet both ring oddly in this world. (I don't know why. It's not because they smell of ritual magic. There's a fair amount floating about. Perhaps because the heroine -- and point of view -- doesn't know their nature until long after she thinks of them?)
Maybe I'll just call it a medallion for its shape.