The word "clocked" can be used to mean "noticed", as in:
Bob: I'm gonna park here a minute. Did you see any traffic wardens about.
Geoff: Actually, I clocked one down the road on my way up.
I'm not sure how widespread this term is, but it's very common here (The Midlands, UK).
I've always thought it a bit of a curious term. Can anyone suggest as to how this usage came about. It is something to do with "time" (i.e. "clocking" someone on a stopwatch)?