The idea of creating very large advertisements and placing them into Earth obit has been very seriously considered. Such “space billboards,” it’s usually estimated, would be about the size and brightness of the full moon and would be visible for hours on end to something like a quarter or half the world’s population at a time. Potentially, no sky on Earth would lack an ad for something.
Current technology is more than enough to do the trick, and actual companies have offered the service (for example, Space Marketing, Inc. of Roswell, Georgia, proposed space advertising for the 1996 Summer Olympics).
It seems that the only obstacles to actual space billboards are:
(1) Public opposition. Any company making use of such advertising would probably (or hopefully) be subject to intense and widespread public criticism. Indeed, I myself can think of few other causes for which I would be willing to go to war.
(2) National laws. At least in the U.S., a law prohibits the deployment of space advertising. Whether, and for how long, the law would stand up to challenges brought to the World Trade Organization, as well as domestic First Amendment challenges, I can’t say. In any case, last week, the FAA asked Congress for the authority to enforce those existing U.S. laws (see CNN.com’s story in their “funny news” section). I believe this is happening now because private space ventures are making rapid progress in the U.S., and the FAA — not NASA — enforces laws relating to private space travel.
Around 1998, I toyed with the idea of writing a screenplay about an underground quasi-terrorist group that sabotage a mission to install some space advertising. They were not the bad guys, either …