We've talked botanigrams before (moss graffiti, guerilla gardening and the like), billboard alteration, and wheatpasting, but here is another version, clean tagging or reverse graffiti. This version, by Paul Curtis, is paid for by advertising agencies, and riffs off those who've been writing messages in dirt for years. Using graffiti styles as advertising isn't new, unfortunately, but creative types are happy to steal back methods that have been lifted from street artists.
Using cleaning brushes (or in some instances, power washers and stencils), tagging or drawing into grime does have the allure of things that have been touched or used a zillion times. Picture the worn and darkened wood of your grandma's trowel handle. It can be that beautiful.
But it doesn't mean I have to give up spray paint!