Audi put up a billboard along Santa Monica Boulevard in Los Angeles, CA to promote the 2009 A4. As you can see from the picture, it read "Your Move, BMW." Thus BMW made its move and purchased a nearby billboard for a response that said "Checkmate" and featured the M3.
Now Audi is prompting its fans on Facebook to suggest their own responses. Facebook users can post a response on Audi's Facebook page. If the response is deemed particularly clever, Audi will contact the user. We're hoping Audi will also post the response on another billboard and keep the billboard war raging.
Audi has managed to turn the billboard war into an interactive ad scheme that is sure to keep the message boards entertained. To see the responses or submit your own check out Audi's Facebook page or check back with Jalopnik, which will post some of the better responses later in the day.