If you walk around the streets, wherever you are, & look down, a clean surface is rarely what you see. The streets are becoming dirtier & dirtier. CURB are a natural media company that have taken the dirty streets & used them as a business opportunity. It is called reverse graffiti, or 'clean advertising'. Instead of adding paints or spraying to surfaces, CURB remove dirt to form advertising slogans. In their words it is "the process of selectively removing dirt from high-footfall areas to reveal an eye-catching message." This new way of advertising, in my opinion, is pretty ingenious; it is a non intrusive, semi-perminent way to engage the public & grab attention away from the traditional ways of advertising. I would certainly pay attention to this, just keep your eyes down.