Over the weekend, the biggest unauthorised takeover of outdoor ads occurred in 10 UK cities over 2 days involving 350+ pieces of subversive artwork. The movement is part of “Brandalism" which is a campaign against corporate take-over of public space. If you visit the site, Brandlism offers instructions for how artists and activists can employ similar ad takeovers in their cities.
from here :http://www.woostercollective.com/post/jade-riveras-painted-tree
check it - http://www.markpowellartist.com/