Just my 2 cents as en entry level collector, but I've found a lot of Lincoln cents in all relevant decades that have enlarged mint marks like this. Usually each one results in a lot of inspection and Google research. This looks like a PMD
"smush" to me, where the S has been mashed by something post mint like in coop's image. There don't appear to be any doubled lines marks at all, DDO
, RPM, or MD. It does give the appearance of the S being upside down, but I think it is just PMD
. I wouldn't offer an opinion if I hadn't seen this so many times and dismissed it after an hour of searching. Happy to be corrected by the bona fide experts!