It's Greek. You don't get ps word initially in Latin. It may have come through Latin as many a word did. There's a play by Plautus called Pseudolus. The title character is a smart slave. This is the basis for the Zero Mostel character in the movie of the Sondheim musical A Funny Thing Happened on the Way to the Forum. I have a dictionary of Late Latin; I'll take a look-see.

Ceci n'est pas un seing.