Coinsandcanada.com

I was reading a prior post here about serial numbers and didn’t want to pollute that thread with my question.

How are serial numbers applied onto bills? Are they stamped on, thereby leaving an indentation? Or are they applied in a way that leaves no impression?

Serial numbers are applied after the bills have been printed by a special press that has numbering machines that rotate after each impression changing the number. As the bills are printed using lithographed printing (you don't state what year you are inquiring about so I will assume that it is for modern currency) which leaves no indentation as the ink sits on top of the substrate, the numbering machine imbeds the ink into the currency so it is possible that you can get a slight indentation as you put it if their is a little too much pressure on the press.

So if no indentation is left and assuming someone could thoroughly remove all traces of ink, how could anyone discern between a bill that has been altered and one that has never been imprinted in the first place?