An MC# stands for a Motor Carrier number. It is a number that allows carriers to cross State lines and it also allows the government to track freight brokers through their system. The docket number is assigned to motor carriers engaging in interstate or foreign operations. It consists of the prefix and the numbers that are issued sequentially as carriers are registered in the system. The docket number is found in the Licensing and Insurance (L&I) database of the Federal Motor Carrier Safety Administration (FMCSA). Most numbers are prefixed by "MC", which stands for 'motor carrier.' Other prefixes are "MX" for a motor carrier that is owned or controlled by a citizen of Mexico or a person domiciled in Mexico, and "FF", for a freight forwarder.