Looks like it is SA marked with a D barrel and Arshins crossed out so it was reworked at least twice in it's life. There is some gunk under the sight - what is that?
All in all a cool old gun that saw lots of use. As to value, nice old guns like this should be around $450 to $550 if everything is in working order. The wear is pretty extreme, overall the condition is fair and there are no bore pictures so I'm fairly comfortable that it is max $550 although it could go higher by a touch if the Remington cartouche is still there and the cocking knob S/N matches.
I recently sold a NEW for $475 but it was in great shape.