I wonder if this is something that was somehow created outside of the mint. It looks perfectly normal on the back but the front looks double stamped but I'm really not sure about it. Maybe it's an imprint or something? I just searched through thousands of pennies, and you find some gross and weird stuff on some of them.
It's what is known as a "vice job" or "squeeze job". PMD. The dead give away is that the letters are reversed and incuse.
Other than reverse letterings, not too bad for a vise job. The reverse doesn’t show much squish , but picture doesn’t show the whole coin. E for effort
Because the lettering is reversed you can imagine a coin being squeezed in a vise onto another coin, giving you the mirror image. If it was struck twice somehow at the mint, the letters should read normally.
The reverse could have been protected by a piece of leather or wood which would absorb the force of the impression.
I agree it's glue but acetone won't budge this bugger. I'd just spend it, why even bother to try to get it off? All he needs to know about this one is it's not an error.
I was attempting to explain how it could have occurred without damaging the reverse if it was a vise-job.