The tuned up blue one, also the grey Mitsubishi and the golden/orange-metallic car with airbrush are owned by US-citizens, so surely US-versions, too. The first two had the old style plate for private cars of US soldiers in Germany, the airbrush-car the new version. "HK" is for cars from the USA (so the plate is in US-size). Private cars of US-GI's, which were bought over here, have (German sized) plates with "AF", "AD" or "IF".