DOT Tire Date Code
All tires come with a U.S. DOT Tire Identification Number. According to the NHTSA, it is:
This number begins with the letters "DOT" and indicates that the tire meets all Federal standards. The next two or three numbers or letters are the plant code where the tire was manufactured. The last four numbers represent the week and year the tire was built. For example, the numbers 3107 means the 31st week of 2007. The other numbers are marketing codes used at the manufacturer’s discretion.