MM = some acronym I never heard of as a coin collecter, oron an online search. I think auctiontech is simply trying to tell you, it appears to have a mint mark. Looks like an "s" to me from pics, so he is trying to say (albeit in coded tongue) that you should include the Mint Mark Letter (P if no letter on coin) in the listing. He goes around all the coin auctions saying this .... thought this might help as he has been all over doing this and if confuses EVEN those who have been collecting ... I guess making random acronyms is quicker and makes people look cool :-) Just kidding auctiontech ...lol