We keep referring to the leader of the international terrorist group called Shadoloo as M Bison. What really does M stand for?
Originally, the M. stood for "Mike". The character we know as Balrog was named Mike Bison, and was a Mike Tyson expy (exported character). Fearing a lawsuit, Capcom shuffled the names of Balrog, Vega, and M. Bison. The closest I've found to a canonical reference to what the M. stands for is in Street Fighter Alpha 3, where
He refers to himself by the full title of Master Bison ("Vega-sama" in the Japanese version), with Cammy and the Dolls referring to him in the same way as well.
As a side note, despite a similar name in Japan and the same fighting style and backstory, Mike of Street Fighter is a distinct character from Balrog.
Though the "M" originally stood for "Mike" in Japan (for the boxer character), Capcom has never explained what it stands for in Western releases, calling it "part of the character's mystery".
His name stands for “Mike Bison”, but is abbreviated for copyright.