Well, everyone in my family knows what the plant is, but my parents taught at Columbia University in the 1960s and they had a very reasonable attitude toward smoking so us kids were casual smokers as well.
Fast forward to this Thanksgiving, and my brother brings his wife and niece over -- he knows I have a little grow going in the apartment. My 7-year-old niece is of course very curious as to what I'm doing, so I tell her these are my Mexican tomato plants and its an experiment. She's cool with that.
But my sister-in-law who is EXTREMELY conservative and sheltered took one look at them and said "Really? It looks like marijuana to me." She would have gone to her grave thinking they were Mexican tomato plants if I hadn't started laughing. But she did see them for what they were.
If SHE can tell they're marijuana at a single glance, so can 90% of the U.S. population. Maybe someone's old grannie can't. But in a country where most people think it should be legalized, you can bet they know what it looks like.