First time I ever heard the word was an episode of Home and Away, early 90s I think. Two characters (forget their names) drilled a hole in the men's shower room so they could peek into the girl's shower room. They look through it and apparently a girl is in there already, naked and everything. Some other guy wanders in and asks what they're doing. They tell him and he says to "Give us a squiz". He looks through the hole. Turns out it's his girlfriend in there and he beats the shit out of the two guys, if i recall.

I told my friends about the episode, and "Give us a squiz" became our go to phrase whenever someone snuck in some, uh ... "professional modeling photography" to school.