Significat

1. to clock in (US), clock on (UK), to punch in (US); (leaving) to clock out (US), clock off (UK), to punch out (US) (to enter or leave a workplace by punching a time card)
2. to record, file, index (make a record of information)
3. to book, to put on file (arrested), n the crosshairs
4. (colloquial) to have your eye on
5. to sign, to sign up