You guys know that on EA's site, they're (or were... I don't know) having a contest for someone to make an ad for the billboards. It was called something like "leave your mark".
edit: i am so glad that the ads do actually blend with the game as much as they do what server were you on? i am thinking that maybe the adverts only turn up on certain servers such as the EA and dice ones, and people who pay for their own don't get them