When you see someone walking down the street wearing a band t-shirt, which band would give away that person as a stoner the most? In my opinion it would have to be Phish, but Widespread Panic and Gov't Mule are close seconds. At this point the Grateful Dead have become pretty mainstream.
I'd say probably Phish, they were popular, but not so popular that you'd really be exposed to them unless you were a pothead. I'm a hardcore Deadhead, but even I have to agree that they've become mainstream and that a good percentage of non-stoners may like them. Bob Marley gear is ubiquitous around college campuses and high schoolers, especially for people who want others to think they smoke.