The "DOT" symbol on commercial tires certifies the tire manufacturer's compliance with the U.S. Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) tire safety standards. The DOT serial number located on the inside sidewall near the rim. The letters “DOT” are followed by eight to thirteen letters and/or numbers that identify where the tire was manufactured, tire size and the manufacturer’s code, along with the week and year the tire was manufactured.