british english

Ah, yes, well. The OED (all editions) lists entries with -ize suffix. There is an entry for -ise, but it is merely glossed as a variant of -ize. If one is to apply the etymological fallacy pedantically, one ought to observe that the French did not invent the suffix (i.e., it isn't from Latin). It is Greek in origin, where a zeta is used.

Ceci n'est pas un seing.