Role-playing in public
In high school, I briefly participated in a role-playing club, and we occasionally met in vacant classrooms, during study hall, or in the cafeteria. Not quite public spaces, but we were exposed to the general student body.
During my freshman year of college, I managed to recruit much of my entire floor to briefly play, and for the most part, people didn't mind stepping over gamers in the dorm lounge. In graduate school, a few friends and I role-played on the National Mall, near Capitol Hill and Union Station, but most passers-by must have thought that we were studying or having a picnic.
I've met gamers and had full-blown conversations about science fiction, fantasy, and comic books in restaurants, on trains and in buses, and in shopping malls and bookstores. Sure, some bystanders might do a double take, but very few seemed offended. On the other hand, we tried not to be obnoxiously loud, tended to play heroic campaigns (rather than those in which we might say, "And then I eat the roast babies for Satan"), and we tried to be friendly to any who had questions about what we were doing.