Don't know where to put this, but... Why not sell advertising on the billboards in Metropolis? Movie posters, TV shows, maybe even Nike could be done...
I'm guessing it would have to get approved by way too many people. DC won't even let us use green auras, do you think they'd be okay with billboards for the next Avengers movie being everywhere in their game ?
Allowing ads on the game's 3-D models tampers with the style/design though. The obvious solution would be to set strict rules on that... but in my experience, once you open real estate up to sales, design goes out the window eventually. The ad people will also get the analytics people involved and we'd be loading some tracking data as well... more info transfer = more disconnects. Ads are evil!
Don't think you'd ever see anything like that in this game. This game is an officially licensed product meaning a company (SOE) have purchased the rights to develop and MMO using characters and intellectual property from another company (DC Comics). What they would effectively be selling is advertising space on another companies intellectual property. If this game was an original SOE creation with original SOE characters, then they would be able to.