UPDATE:

Many thanks for your concern which is well understood. Please be assured that the Embassy took appropriate measures immediately. @PoPville — German Embassy (@GermanyinUSA) August 15, 2017

“Dear PoPville,

In light of the protests in Charlottesville this weekend, we were pretty shocked to see this collection of bumper stickers on the highway down to Richmond. Upon closer examination we noticed the diplomatic plates. The internet says diplomatic license plates in the US are issued in a specific letter format, which identifies this car as a non-diplomatic staff member (S) for Germany (LW)! Do embassies have rules or recommendations against this kind of expression?”