In September 2006, the mayor of Sao Paulo passed a "Clean City Law," which essentially outlawed all outdoor advertising. 15,000 ads had to be removed, and store signs had to be shrunken down.
A NY Times article from 2006 described the implications of the ban as such:
Photographer Tony de Marco took the following pictures in 2007:
And here are some before and after shots:
According to an article from newdream.org, everyone seems to be pretty pleased with the ban: