It makes city governments cringe. But graffiti can be provocative, inspiring and poetic—sometimes even a tool for public discourse. That's what San Francisco designers Axel Albin and Josh Kamler say in their new book, "Written on the City." They've compiled their favorite "message graffiti" from cities around the globe—the musings, rants, political statements and cultural observations of artists who risk jail to have their voices heard. The best examples are poignant ("One week that we've been separated," reads an image of two lovers), funny ("You looked better on MySpace," jokes another) and thought-provoking ("Create beautiful children. Marry an Arab," says a wall in Tel Aviv). The original spray paintings are likely covered up by now: cities spend millions each year to do so. But the authors believe their photographs can tell us something about the dialogue happening around us. "People want to talk about graffiti as this kind of raw, urban, danger-of-the-city kind of thing," says Albin. "But this project is really more human than anything else."