I'm certainly not an expert, but I don't think that I have ever seen a Mickey Mantle autograph where he has "dotted" the "i" with an "o" before like in the referenced auction.
http://www.daileyauctions.com/fullpic.php?picid=2861
The rest of it looks sloppy to me, but that "o" on the "i" just jumps out at me.