Title says it all. If you had the opportunity to advertise ANY TES game your shrivelled black heart desired, how would you do it?
For Oblivion, I just would not be able to resist the urge to have people dressed as Dremora walking the streets. Merhrunes Dagon has invaded Earth! Maybe a projection of him on a building would be awesome, too.
As for Skyrim (this one is mostly just to screw with people ) I would have a LOUD speaker on top of a building that bellowed out dragon sounds. Nothing like a little mass panic to get you into TES V