So based on the above, is it fair to say a basic (non destructive - since I don't think you can look at the bare metal most times 
) inspection of whether the stamp seems to be at the exact same surface of the paint it is applied to would be a half decent way to tell? Rubber stamp would seem to be at the exact same surface, no difference from paint surface, while heat stamp may show a bit of a depression as described above?
Obviously harder to tell if the unit is not in pristine condition, but for something not dirty, etc., it might be possible to look at an angle and see if you can discern any difference in the surface of the lettering vs the paint itself.
-Dave
