One time he walked into a few different famous art galleries in disguise and hung some of his art up on the walls between all the other famous art. It was a while before they were noticed and a few of the galleries let his work stay up.
http://www.woostercollective.com/2005/03/a_wooster_exclusive_banksy_hit.html
http://www.woostercollective.com/2005/03/a_wooster_exclusive_banksy_hit.html