Means to notice or recognise someone, especially when they’re trying to blend in or pull a fast one. If you’ve been clocked, you’ve been spotted and your little plan’s basically done. Works for people, dodgy behaviour, or even tiny details you suddenly twig. You’ll hear it in pubs, on the street, at work, anywhere you’re keeping tabs.
"I tried to nip off early, but the boss clocked me hovering by the door, so I legged it back to my desk."