It is a code used, among other things, in Maryland, Michigan and Minnesotta, to calculate your licence based on your personal information.
"A number of states encode your name and date of birth in your license number. These include Maryland, Michigan, and Minnesota (prior to December 13, 2004 only). These states use the same system of encoding, or very similar ones. Given someone's driver's license number from one of these states, you can take good guesses at someone's name and exactly determine day of birth (but not year). With someone's name and date of birth you can guess some or all of their driver's license number."