49 CFR §215.303

1. (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—
   1. (1)In clearly legible letters; and
   2. (2)In accordance with paragraphs (b) and (c) of this section.
2. (b)The letter “R” shall be—
   1. (1)Placed immediately below or to the right of the car number;
   2. (2)The same color as the reporting mark; and
   3. (3)The same size as the reporting mark.
3. (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:
   1. (1)Age.
   2. (2)Coupler.
   3. (3)Draft.
   4. (4)Bearings.
   5. (5)Truck.
   6. (6)Underframe.
   7. (7)Wheels.
   8. (8)Yoke.