Here's the breakdown on the DOT tyre manufacture and date codes. Tyres made before 2000 use 3 numbers and tyres made since 2000 have 4 numbers. If your tyre does not have this style of code it is either non-DOT approved or too old in which case it is unsafe to use.
The tyre shown here will be a Kumho KU31 Ectsa SPT. DOT H2WP YC9J 0811
DOT = Tyre meets DOT safety standard.
H2 = DOT's tyre plant code
WP = Tyre size code
YC9J = Manufacturer symbol identifying tire brand
0811 = Week and year tyre was made - 08th week of the year 2011
For a list of tyre manufacturer's locations:-
http://www.harriger.com/tire6.htm
For the record, the tyre above was purchased from Tempe Tyres (which many have parrallel imports warnings all over them from conspiracy theorists), or (old tyres warnings etc). But as you can see, they are built in Korea and are only 32 weeks old.
My Kumho KU36s have a manufacture plant code of Y0 = Korea.
Hope you find this useful...