Kissing on the quad, briefly WSJ Crossword Clue

Think of three letters that capture a romantic gesture in open spaces.

??? stands for 'Public Display of Affection,' which refers to physical acts of intimacy in public.

The clue refers to 'Public Display of Affection,' which is often abbreviated as '???.' Kissing on the quad, a public area in a school or college, is a typical example of such a display, hence the connection to the abbreviation.

Subway smooching, e.g., in brief, K-I-S-S-I-N-G in a tree for all to see, for short, What might cause someone to say, "Get a room!," for short, Common sight at an airport drop-off, in brief, Bussing on the street, e.g., in brief