A reporting mark is a code used to identify owners or lessees of rolling stock and other equipment used on certain rail transport networks. The code typically reflects the name or identifying number of the owner, lessee, or operator of the equipment. In North America the mark, which consists of an alphabetic code of two 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 it is traveling over, which shares the information with other railroads and customers. In multinational registries, a code indicating the home country may also be included. 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. Railinc, a subsidiary of the AAR, maintains the active reporting marks for the North American rail industry. 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. Marks ending with the letter "X" are assigned to companies or individuals who own railcars, but are not operating railroads; for example, the TTX Company (formerly Trailer Train Company) is named for its original reporting mark of TTX. In another example, the reporting mark for state-funded Amtrak services in California is CDTX (whereas the usual Amtrak mark is AMTK) because the state transportation agency (Caltrans) owns the equipment used in these services. This may also apply to commuter rail, for example Metrolink in Southern California uses the reporting mark SCAX because the equipment is owned by the Southern California Regional Rail Authority—which owns the Metrolink system—even though it is operated by Amtrak. This is why the reporting mark for CSX Transportation, which is an operating railroad, is CSXT instead of CSX. Private (non-common carrier) freight car owners in Mexico were issued, up until around 1990, reporting marks ending in two X's, possibly to signify that their cars followed different regulations (such as bans on friction bearing trucks) than their American counterparts and so their viability for interchange service was impaired. This often resulted in five-letter reporting marks, an option not otherwise allowed by the AAR. Companies