Start of many emoticons

COLON

Look for the punctuation mark that often precedes a smiley face in texts.

This clue plays on how many text-based emoticons begin with a colon, like :) for a smile or :( for a frown. The word "start" hints at the first character, and "many emoticons" points to the colon’s common role in them. It’s a straightforward definition where the answer is literally the punctuation mark itself.