41 CFR 102-34.100 - Where is motor vehicle identification displayed?
Motor vehicle identification is displayed as follows:
(a) For most Government motor vehicles, preferably on the official U.S. Government license plate. Some Government motor vehicles may display motor vehicle identification on a decal in the rear window, or centered on both front doors if the vehicle is without a rear window, or where identification on the rear window would not be easily seen.
(b) For trailers, on both sides of the front quarter of the trailer in a conspicuous location.
Each agency or activity that uses decals to identify Government motor vehicles is responsible for acquiring its own decals and for replacing them when necessary due to damage or wear.