The DOT stands for the Department of Transportation, a government agency required to certify quality standards for vehicles. This DOT certification is branded on the sidewall of your tire, which certifies that it meets or surpasses the requirements of the DOT. The numbers/letters that follow the DOT mark represent the plant where the tire was manufactured, the size, pattern, brand, and the date of manufacture. Federal regulations encourage registration of each DOT number for every tire purchased.