It's a 686-1 and has been back to Smith for work. That's what that hyroglyph means between the SN and model, right?
SOME of the 686's were sent out before the recall. Those were returned and given a stamp. Later guns had the recall done at the factory so they came with the M stamp. The 2 below were CS-1 guns, Customs Service. They were returned a to be checked that the recall was done.