Your vtec sulenoid is located to the left of your exhaust cam (DOHC). On SOHC, it's right in front of your distributor. That's the best way I can describe it. Just look for the sulenoid, and that usually means they are running vtec... unless they have it turned off (vtec controller) or their check-engine light is on, or the car is cold, or the oil pressure is low... So yeah....
Just curious, why do you ask?