I have a little story to tell:
This last friday night, I was smoking a joint with a buddy of mine. We were cruising around for a while, then we were relaxing in my screen porch, finishing off the joint, when I remembered that my parents might be back any minute. As soon as I put the joint out and went back inside, my parents came home. I had a brief conversation with them, they commented on my looking "really tired" (my eyes were as red as Satan's cock), and we just told each other good night and I didn't get caught.
So I guess they couldn't smell it on me, and they think that I'm too good to smoke weed, so I don't even know if they know what it smells like. But weed does have a distincitve smell, and if they smelled it I'm sure they would've made a comment.
I think that only if you get smoke blown on yourself or if you get ashes rubbed into your clothes, that's mainly how they'll be able to smell it on you. I myself was in a well ventilated screen-porch, so the smoke never lingered. Just make sure when you smoke it, the smoke doesnt have a chance to linger for too long and you won't smell like weed. Give yourself ample time before you encounter your parents just to be safe, but I'm sure it doesn't take a ridiculously long amount of time for the smell to go away.