Instead of the original L that would occupy the top screw hole on the lens mount of a M camera, the one I just purchased seems to contain a Y. The camera is located in the USA and the best I can guess is that it would likely serviced by Youxin Ye? Can anyone confirm that this is his mark?
Side note the camera appears to be in BEAUTIFUL condition and I will post photos of it when it arrives.
Here again, I'm just taking it at face value, so you may want to track down a more authoritative source than this. However, the info in that post is supposedly taken from the book '25 Jahre Leica Historica'.