Definition from Wiktionary, the free dictionary
From Latin sigillum.
sigil (plural sigils)
- A seal, signature or signet.
- A sign, image or symbol considered to be magical.
- (programming) A nonalphanumeric character affixed to a symbol (e.g. variable) to indicate a property such as type or scope.
Derived terms 
seal, signature or signet
computing: character affixed to a symbol