City sidewalks and curbs are filthy, and U.K.-based Green Street Media, which provides "sustainable, eco-friendly advertising solutions," takes advantage of this in a clever way. When a client wants a sidewalk advertisement, rather than using chalk or spraypaint GSM uses laser-cut stencils and a high-pressure hose to blast a clean spot out of the stencil's negative space. The only materials used are the stencil and plain water.

GSM estimates that depending on foot traffic, in 3-5 months the advertisement will fade as the sidewalk goes back to being its filthy old self.