Not even when the person is Willy Nelson?
Unless he was actively smoking weed, or the room smelled like weed, probably not. I not Willy is a pot head, but if I were to meet him pot would not be on my conversation list.
My point is this: people are more likely to notice what they are familiar with or interested in. I might be looking for guns, but I wouldn't be looking for drug paraphanelia.