I bet more people are hiding it by being normal, every day people than you would think. It's NORML to smoke pot! Hahahah, but its so true. Of course you can usually tell when people smoke thanks to people perpetuating stereotypes like dreads, tie-dye, jam bands, etc., but they are not the only people that smoke marijuana. Another good thing is to not smoke before things like work, as someone said above. If you dress nice and are personable, no one will suspect you of smoking marijuana in your free time because it doesn't change who you are as a person.