Reporting mark
A reporting mark is an alphabetic code of one to four letters used to identify owners or lessees of rolling stock and other equipment used on certain railroad networks.
In North America the mark, which consist of an alphabetic code of one to four letters, is stenciled on each piece of equipment, along with a one- to six-digit number. This information is used to uniquely identify every such rail car or locomotive, thus allowing it to be tracked by the railroad they are traveling over, which shares the information with other railroads and customers.
Standard practices
North America
The Association of American Railroads (AAR) assigns marks to all carriers, under authority granted by the U.S. Surface Transportation Board, Transport Canada, and Mexican Government.
Under current practice, the first letter must match the initial letter of the railroad name. As it also acts as a Standard Carrier Alpha Code, the reporting mark cannot conflict with codes in use by other nonrail carriers.