That is the DODAAC. The Department of Defense Activity Address Code
(DoDAAC) is a six position code that uniquely identifies a Department of Defense unit, activity, or organization .
For instance, when ordering parts, a unit is ID'ed on a requisition, by the DODAAC, and not its real title. A real title can be confusing at times. Every unit has a DODAAC. When parts are sent to the unit, they are separated by DODAAC, and there is (superposed to be, anyway) no way they can be mixed up.