The use of symbols for magical or occult purposes has been widespread since the Neolithic era. The term sigil derives from the Latin word sigillum meaning seal.
Sigils are a type of symbol used in ritual magic like a pentagram that is drawn or painted on a wall, ceiling or floor to offer either protection or a short cut to particular spell work; they are also used as messages or warning to others. They come in many forms and are encoded with your will and intent which gives them the power to work; the most powerful sigils are drawn in blood.