Anything about a 12 gauge shotgun with Robinson Bros and Co stamped on it also says nitro reliable?

The Robinson Brothers and Co. were gunmakers based in St. Louis, Missouri, USA, who were in business from 1875 to 1932.

The "nitro reliable" marking on your shotgun indicates that it is chambered for nitro-cellulose propellant, which was introduced in the late 19th century and replaced black powder as the standard propellant for firearms.

The marking suggests that the shotgun has been proof-tested and is safe to use with nitro-cellulose ammunition.