Why can't Debian do the same thing that is done with US export licenses? Don't put restrictions on use of the logo bitmap, but say "note that this does not excuse you from obeying the law, which prohibits you from using the trademark to identify your product..."
Just make it clear that the license allows use of the logo in the sense that a user of the logo won't be sued for copyright violation, and does not address other reasons why someone might not be allowed to use the logo.
