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!
Cheers!