I actually did send it in to PSA a couple years ago and they could not guarantee authenticity on the signature so I didn't have the card graded with a qualifier or anything.
Really? That is surprising but they obviously know something we don't. I know the "M" is similar to what is deemed as a "thru the mail" signature where someone other than Mr. Jordan opened up his mail and signed stuff and returned it, basically a secretarial signature. See below for example:
Below is examples of Jordans autograph over the years: