Billboard Liberation Front
"Improving" outdoor advertising since 1977. Includes how-to manual for altering outdoor advertising.
Cicada Corps of Artists
"Cicada billboard alteration embraces the idea of using the negative against itself."
Culture Jammer's Encyclopedia: Billboard Libe
Includes gallery with dozens of examples of liberated billboards.
Ron English POPaganda!
Prolific producer of surreal and parodic billboard art since 1982.
Smashing the Image Factory
A complete manual of billboard subversion and destruction. Humorously ranges from the innocuous to the terrorist.