What is a sigil?
– A symbolic restatement of a specific intention, executed in such a way that it sneaks under the radar of the conscious mind and heads into the fertile loam of the subconscious/astral plane/whatever to alter reality. The technique was invented by artist and magus Austin Osman Spare around the dawn of the 20th century. See http://www.flyingfists.org/archives/000450.html, http://www.sigilgarden.com/words.html and http://www.chaosmatrix.org for more information.