I'm not sure what an FM is unless you mean you found it on the road - some minor highways in Texas are designated FM, but that sure is a pretty knife.
If I found that at a flea market, I’d probably buy it too. Ram’s horn? What does the etch on the blade say? Are there any other markings?
Someone spent a lot of time on that file work. Not something like I've ever seen at a flea market here in West Texas.
Butler, PA is a long way from the Rio Grande valley! I used to live in the Shamokin/Mount Carmel area but have lived in South Texas for 15 years now. I see those knives at gun show here. The examples I've examined are made in India though!
To show my ignorance about knives,,, what is the file work ? Is it the serrations on the back of the knife ?