HQ-244
Truck was assigned to Headquarters (HQ).
It was the 244th vehicle of whatever the maximum they were allowed. 300 for example.
Every unit is different on the number of authorized vehicles.
This information is always painted on the right side of a bumper, etc.
Most US Army equipment will have the unit markings.
Vehicles, trailers, generators, pumps, etc.
A quick forum search will tell you the format that is used.
Internet search of bumper numbers will usually yield the unit