Just make lots of weed references/jokes and see if they get them or laugh or whatever...

Like this...

Me: Hey man, what you do all summer?
Some dude I just met: Yknow... nothin much
Me: Ahh yeah... lots of deep breathing and coughing?
dude: haha yeah
Me: yeah me too :dance:

OK that's probably not the best example, but you get the idea... If they have no idea what you are talking about, they probably don't smoke. If they figure out what you are talking about and they aren't cool with bud just say you were talking about hookah...