Thank you for all the Welcome signs, no doubt this is a great community and website.
Great discussions all around on the X marks. I'm lucky to have both the real and fake in my collection. What I will say is the layer of silver is VERY thin on the fake, enough to where you can use your fingernail to chip it off or even a dental pick to expose the iron underneath. It's flaky enough to where it may not even be a silver layer (I haven't tested it yet). You wouldn't have to create a deep gouge in the coin to see what's underneath. The other possibility here is a scratch or hardness test was the reason for the X's, especially if fakes at the time were coated in something not silver.
I'll find some time to test the coating on the fake, see what it's made of and report back.
Attached are photos of a real Morgan with the X's and a fake one with just the silver coating. On the fake one you can see the iron rusting underneath on a piece that chipped off on the cheek.
Spoke with an old-timer about X's on older silver dollars. He mentioned after the war (WWII) when Europe was decimated, a lot of banks, brokers, and dealers overseas would scratch the silver coin to ensure it was real silver and not just a silver coating. Lots of fakes during that time coming out of Asia after the war. So likely if you see those little X marks on a silver coin, it just meant it was used overseas at some point in time during that era.