I don't know what M stands for yet but I have a feeling that I'm on the right track
John Wilkes was portrayed in the movie
Bedlam in 1946 by Leyland Hodgson
The star of Bedlam was Mr. Boris Karloff, most famous for portraying Frankenstein and The Mummy.
My current guess is that one of those two, or the entire UCM, is involved in the marketing or merchandising? That seems pretty easy, though
The only other way that I can see is that Hodgson is most famous for portraying Sherlock Holmes, which could be a kind of cool icon for the event (like the detective origin of Legendary Truth or something)