The railroad or private car owner reporting mark, the car number, and built date shall be stenciled, or otherwise displayed, in clearly legible letters and numbers not less than seven inches high, except those of the built date which shall not be less than one inch high:

(a) On each side of each railroad freight car body; and

(b) In the case of a tank car, in any location that is visible to a person walking at track level beside the car.