In revenge for the intrusion of commercial posters into the public space that is their only forum, genuine posterers counter-attack by appropriating commercial advertising space for their own posters. By doing so, they simultaneously make a political statement, engage in economic sabotage of expensive advertising space, and give their own message greater prominence. The posters pictured below have been carefully placed on Viacom's bus shelter ad spaces to send a message about the underlying ad while piggybacking on it for visual prominence.