Simple question: Why do we need permission from a state bureaucracy to modify public space? As members of the public, don't we have that right? Plus, as Yok and Sheryo have pointed out, isn't it just more fun to carve your own path? Not to sound all libertarian, but public space is a place for the public to define and develop, with assistance from the state. If the state has made a mistake, sometimes the public just has to make it right. The thrill of taking action isn't bad either.
Here's what Sheryo and Yok have to say about it all:
"Ads invade our public spaces and make us feel less about ourselves. Why do they get the right to tell us what to do and how to feel? Our piece for Art in Ad Places is a cheeky public service message that might inspire people to do what they want without waiting for permission to do it. Sometimes it's just more fun to do things without permission. No guidelines, no boxes to check. Just wing it."