That would also mean that merchants all over the world knew about this system and it would have been printed somewhere. And if a fake was found, true, why would someone mark it and then put it back in circulation? Sort of a silly idea. But who knows. There are many reasons for an X on coins and not all are X's. Some are just a line, some curved scratches. As already noted some people did it for no reason at all. Many kids did it when I was a kid. Can't remember why, but we did. If you played games with coins, lagging at lines in the sidewalks, many kids would scratch an X, Y, line, O, etc on thier coins. With maybe 5 or more kids playing it made your coin easily identifiable. Same with throwing coins for distances. We all heard stories about Washington throwing a coin accross a river so many, many of us kids tried to see how far we could trow a coin. Had to mark it so you would know which is yours. Making counterfeit coins in my younger days was normal for many. When I was a kid a half dollar could get you a lot of stuff. One of the methods used a lot was with Lead and little Zinc and/or Tin mixed in. Of course those were really soft so many coins would be scratched to see if those were one of them. Another thing was if you collected coins and you didn't want others to have what you had you would deface as many as you could not afford to keep. An X on them was easy to do.
