There are three terms in French, aucun 'none', personne 'nobody', and rien 'nothing', which started out from Latin and into Old French as positive (< Old French alques 'something' < Latin aliquid 'something' + un 'one', persona 'mask, part; person', and rem, the acc. of res, 'thing') but today are negative in meaning; cf. Old French les riens que j'aime 'the things which I like'. They seem to have gone from positive to negative on account of the formation of the negative in French: ne + V + pas (< Latin passus 'step', actually that's another one, pas can be used in the meaning 'not'), where pas strengthens the negative force of the sentence; cf. English I don't care one bit.

Ceci n'est pas un seing.