I can't find any reference to a tool company's name even remotely resembling these initials. I think the most likely answer is that it was made on contract for a private company to serve a specific application on a piece of equipment. The name would be the initials of the company for which it was made It may be pre-war because of the thickness of the handle and the relatively primitive name stamp style and alignment--makes me think of carbon steel wrenches from way-back-when. Could mean something like "Sam & Pete Machinery Services" or something along that line. Good luck trying to find the name of that (probably) long-dead operation. As far as worth, I think you'd struggle to get even $10 for it--there's so many old wrenches out there (no one ever threw away tools) from recognizable mfrs that sell for very little. There's also lots of 'orphan' tools out there like this one too. No one is likely to want it as a user.
It may be possible to find what tool company made it. You'd have to peruse sites like Alloy Artifacts, going through one old mfr to the next until you find a matching style--I've been successful at that a few times. You then might find a collector of 'XYZ' tools who'll want this unusual variation from that mfr, but even then it may only be worth a few dollars more. Now if we could find what company those initials stood for, and if that company can be connected with something or someone of high name recognition ("this co. was owned by Theodore Roosevelt" or "this company made the engines for WW2 B-29s" or something like that) , it'll go up a few dollars more. Or maybe you'd find someone like "Gosh, my grandfather owned that company! I gotta have that wrench."
For the moment, it's just a wall hanger, $5 to $10 on a good day.