American railroads adopted written timepiece standards after collisions traced to timekeeping failure. The requirements were set by individual roads and general inspectors, so they varied in detail while converging in substance.
Typical requirements include a minimum jewel count, adjustment to temperature, isochronism and several positions, a lever-set mechanism to prevent accidental hand-setting, an open-face case with the winding crown at twelve, a bold plain Arabic dial and a maximum permitted daily variation.
Lever setting is the clearest surviving giveaway: the bezel must be unscrewed and a setting lever pulled before the hands move, which rules out the common failure of shifting the hands while winding.
Inspection created paperwork. Watches were checked on a schedule and rates recorded in inspection cards, so a watch with surviving inspection documentation carries unusually good provenance.
Not every high-jewel watch is railroad grade, and not every railroad-marked watch met a standard. Read the movement's stated adjustments, setting type and dial layout against the standards of the period rather than the seller's description.