Yes, you can lift the “m” off of M&Ms.
I recalled this old trick while in the candy aisle on a post-Easter shopping spree at Target.
M&Ms are made by coating small round bits of chocolate with a candy shell so that, yes, it melts in your mouth, not in your hands (mostly). The “m” is printed after the candy coating has hardened and (I think) been glazed.
To remove the signature letter, take a small cup or bowl and fill it with an inch or two of water and drop in a few candies. In my experience you won’t be able to harvest the letter from each one, so plan accordingly.