My first reaction is that there is no such company, but I looked at the search and it does exist. So there is a company. None of the photos show railcars however.
I worked in an around steel mills for the first half of my career and have friends who also worked in the plants. There may be some exceptions, but in my experience, the steel companies did not own or operate cars in common carrier service. They owned and operated a lot of stuff inside the plants. The gons and general purpose flats and hoppers if any were geneerally used and well worn. If they had any markings at all, it was just a number. I had a friend who worked in the front end area of a major plant, that is blast fce, sinter plant, etc. He told me when they got "new" cars in the first thing they did was cut off all the brake rigging because it just got in the way. This plant in a flat area. Not sure if all plants did this, but I suspect many did. The special purpose cars such as bottle cars, slag cars, and ingot buggies, never left the property, and because of their use with very hot (over 2000f) materials and environment, did not have lettering on when I saw the if ever. The ones I saw had a steel number cutout and welded on the side.
Two steel mill ownend rrs that I think had gons were the Union RR around Pittsburgh, and the Elgin, Joliet, and Eastern around Chicago. Both of these were common carriers and had their own rolling stock. However, even though owned by US Steel, the RRs were separate entities and the equipment was lettered for the URR, or EJ&E, not USX or something similar.
Odds are pretty much against this being a prototype scheme.
