the dis-

It means something like 'apart from'. (In Italian s- < Latin dis- has come to be a rather productive prefix.) These affixes go all fuzzy semantic. For example, the tendency in Romance and Germanic languages (at least) to use diminutive suffixes to connote cuteness and friendliness, while the augmentatives are pejorative. (It just dawned on me towonder if the typical prefix sh- in Yiddish is related.)

Ceci n'est pas un seing.