I got an old bill recently. The color is much darker and the paper feels different. I happened to recognize it as a silver certificate and kept it.
Years ago we got a bill as change in Williamsburg, and it looked strange. We were afraid to spend it in case it was phony, so we called the SS and were told to send it to them. If it were legal, they would return it. We did and a few weeks later it came back in the mail with a letter telling us to take it to the bank to cull. We kept it and the letter. :)
That’s. Very cool!