Stretched across city walls and along rooftops, Stephen Powers's colorful large-scale murals sneak up on you. "Open your eyes / I see the sunrise," "If you were here I'd be home," "Forever begins when you say yes." What at first looks like nothing as much as an advertisement suddenly becomes something grander and more mysterious--a hand-painted love letter at billboard size. Combining community activism and public art, Powers and his team of sign...