One who makes a tick mark.

A measuring or reporting device, particularly one which makes a ticking sound as the measured events occur.

A ticker tape, either the traditional paper kind or a scrolling message on a screen.

(slang) A heart, especially a human one.

(slang) A watch (timepiece).

(birdwatching, slang) A birdwatcher who aims to see (and tick off on a list) as many bird species as possible.