Originally Posted by BrianW
There should be a DOT code on the sidewall with the manufacture date.
Specifically, should be "DOT" stamped somewhere on the sidewall, followed by 4 digits. Sometimes it's only stamped on one side. First 2 digits are the production week (1 through 52) last 2 are the year 01 (4 digit codes started in 2000 or 2001) through 21 (this year).
If there is only 3 digits, tires were made prior to the 2000/2001 switch to 4 digit codes. Most of the info applies the same, the first 2 digits are the week, last digit is the year.