Bicentennial ike dollar version 2, with odd mint error. Looking for insight.

I have a Bicentennial Ike dollar, and on the reverse side just left of the liberty bell and under the U in United, there is a raised letter M in a script style. There is probably a very interesting story behind the M, just wondering if anyone knows anything about this minting error? If you turn it upside down it could also be a W.