Win. 1897 Riot ?

Just picked this one up. The guy I purchased from believed it to be a Trench-Gun. I don't, but I liked it so I got it anyway. Take-down model. Has 24" FULL choke barrel, matching serials,4574xx which I believe to date from 1910. But the reason I liked it is the marking on the right side of receiver / 9 MA X /. Which I don't have a clue what this stands for. Law Enforcement, Unit Mark ? :dunno: No other markings besides the norm. Anyone got any Ideas?

JLS
https://www.milsurps.com/images/impo...g?t=1263680085 https://www.milsurps.com/images/impo...g?t=1263680138