A mark that carries meaning by being recognised rather than read. A sigil belongs to what it marks, and is not taken lightly.
Latin sigillum (a small seal, an image), a diminutive of signum (a mark, a sign); a mark that carries meaning by being recognised rather than read.
A mark that works on sight rather than on reading, so its meaning survives whoever cannot read the language around it — and because it belongs to what it marks, using one is a claim, not decoration.