I can't quite make out that first letter stamped on your link but it does resemble a R as to what railroad R&S stands for I have no idea? Maybe if you rubbed a little bit of light oil into the stamped letters it might be more recognizable? The book The American Railroad Freight Car by John H. White Jr. has some interesting and very good info with some diagrams and pictures of draw heads, link & pins, journal box covers ect. I've always loved the old RR iron and got hooked on hunting for it a good 30 years ago. Old railroad right of ways are littered with the stuff, but of course most are buried. Rivers, streams, creeks and culverts are where lots got discarded. On page 490 in Whites book he mentions how one small RR lost over 43 thousand link & pins in one year alone! I have found lots of link & pins over the past 30 years and have lost count. I have given many away to friends over the years. Attached is a photo of a 55 gallon plastic drum full of them in my barn I still have, I found a couple this past summer in the river when the water was low. I also have a old RR signal relay cabinet full of my good ones on the shelves, some are marked ones. I think I found my first ones while out metal detecting a local mid 1850's RR grade. I have found more that were tossed into rivers, streams ect. One local river had 3 RR lines, 2 crossing over it and one running along side it, and that river was a major dumping ground for discarded RR iron. Link & Pins still turn up each year from the changing river current and from flooding. There are probably fewer marked link & pins out there but I have found several. Of course the iron being buried or in the water for the past 120 -170 years doesn't do much for being able to see any good markings. A lot depends on the soil or water condition. These things traveled all over the country on different RR's! In my photo you'll see a broken coupling pin laying in the top of the barrel with UP / Union Pacific stamped into it with pretty good stamping. I found that in the river at Monroeville, Ohio about 4 years ago, that ones a long way from home!. About 10 years ago I found a coupling pin in the river at Elmore, Ohio with nice stamping having N C & ST L from the Nashville Chattanooga & St. Louis RR. I have found some stamped with B&A, NRC, and others along with more local RR's from the C&T, LS&MS and NYC RR, and B&O RR. The B&O RR ones I have are a bit interesting as they are a much older type of links and pins and the letters are raised and not stamped. I also have a good 100 or so RR marked journal box covers, many early bolt on style and also the hinged style, I like finding those the best. The RR's must have loved marking their old iron. For me it has been a interesting hobby hunting and looking for the stuff. I know of a few collectors of the stuff, and one will see the stuff occasionally on Ebay and I have bought a few pcs. over the years but i'd rather go out hunting for it. I'm 60 now so I don't get out like I used to down in the underbrush along the old grades with a detector or jumping in the rivers like a water dog but it has been fun. I'm a RR engineer and I retire in less than 3 years. About 20 years ago 2 different times while on slow coal trains I spotted coupling links down in the ditch from my side window. I went back and got them after I got home. Both links were not stamped. It was neat spotting and finding those! Happy hunting!