As an old habit I drop/bounce the front wheel on any bike I get my hand on. I can hear a slightly loose headset a mile away. It rattles slightly instead of sounding solid. I verify with a brake grab and front wheel rock while holding my hands over the headset cap and frame to feel for movement.

Also helps diagnose loose wheel bearing adjustment. If the headset is tight but you heard a rattle then grab the rim and wiggle side to side to check for play.