The NATO Status of Forces agreement is always being challenged & renegotiated. Polizei harassment of American G.I.’s is an old tactic to this end.
As an aside, in 1982 they changed USAREUR license plates from green & black to white & black to make them `blend in’ with German tags & less recognizable to terrorists (right!).
Polizei are organized under the respective German states & are equivalent to our state highway patrols. Now, they are DEATH on DWI & a drunk driving Strafsbefel from the Polizei goes straight to one’s general officer HQ command, usually resulting in a field grade Article 15 which is a career killer.
A USAREUR driver’s license is issued after one presents a valid state driver’s license & passes a written test on German traffic law & signage. Therefore there should be no need for the Polizei to see a domestic U.S. driver’s license.
Again, this is petty harassment disguising a larger issue. The fine East German hand of Bundeskanzler Angela Merkel may be at work here.