Years ago, maybe 1977 or 78 a fellow showed up in our office selling portable check embossing machines. Those are the ones that punched a series of tiny perforations in the amount line of the check, to make it less likely to be forged.
As part of his sales pitch he had us write out a check and within 3 minutes he had put a solution on the check and washed all the ink off.
He left our signature on it by taping over it before the washing started. Then he made it out to himself with a million dollars on it.
We bought the embossing machine on the spot.
He also showed us how to forge checks. If you try to copy someones signature your own style of writing tries to take over. But if you turn it upside down, and replicate it you will eventually become a very good forger. Try it sometime.
It looked like the one below. It cost something like $995, way back then. It certainly wasn’t in our budget, but we didn’t need to have someone forge one of our checks for a million dollars.