I've seen many instances of flags on the right side of vehicles with the union facing backward -- it's common on police cars, for example. The same is true of flag patches on non-military uniforms (scouting organizations, sports teams, etc.). Military regulations state that it should be forward, but as far as I know there is no corresponding civilian rule.

I suspect that the reason for the "backward" flags is economic: most flag decals and patches are made with the union on the left, and people apply them without any regard to which way it's facing in relation to the direction of movement. Again, there's nothing wrong with this per se; the flag code does not address the subject one way or the other.

Peter Ansoff