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:
The outsized billboards and screens that dominate the skyline, promoting everything from automobiles, jeans and cellphones to banks and sex shops, will have to come down. All other forms of publicity in public spaces, like distribution of fliers, will also stop.
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:
Five years later, São Paulo continues to exist without advertisements. But instead of causing economic ruin and deteriorating aesthetics, 70 percent of city residents find the ban beneficial, according to a 2011 survey. Unexpectedly, the removal of logos and slogans exposed previously overlooked architecture, revealing a rich urban beauty that had been long hidden.