I think this could be invaluable PR. We could volunteer at a place with large fluxes of people, some highly public place. We could advertise ourselves with a banner. As we swept floors / served food / whatever, we could meanwhile do the same thing we do anyway: talk. Most importantly, we would wage righteous mortal combat with our cursed foe, that most pernicious and widespread belief that atheists are less moral, less charitable. Actions speak louder than words. Alternately we could all collectively piggy back onto a volunteering meetup, but still show up as a group, banner in hand. I'll chip in on the legwork, but I'd first like to know if others are with me.