And say you are ticketed for obscuring your plate with a rack. Then what? Just because a cop does it doesn't mean it is OK.
Well, actually … police are supposed to conduct themselves in a way that reflects all laws, at all times except for emergencies. So yeah, if the cop can do 'it' in a non-emergency situation, then Joe Citizen should be able to take that as being safe, legal behaviour. "It" includes speeding, lane selection, obeying traffic signs/signals, and yes that's right, display of license plates.
Emergency situation can be easily identified as lights/siren activated. Anything else is non-emergency.
When one person suffers from a delusion, it is called insanity.
When many people suffer from a delusion, it is called religion.