49 C.F.R. § 215.303
(a) Each restricted railroad freight car that is described in § 215.203(a) of this part, except for railroad freight cars used exclusively for tourist, historic, excursion, educational, recreational, or private purposes and that are not interchanged, shall be stenciled, or marked—
(b) The letter “R” shall be—
(c) The following terms, to the extent needed to completely indicate the basis for the restricted operation of the car, shall be placed on the car following the symbol “R” in letters not less than one inch high:
[44 FR 77340, Dec. 31, 1979, as amended at 91 FR 22738, Apr. 28, 2026]