|What's Wrong With This Picture?|
In case you need to be pointed in the right direction on this one, you might want to look into the origins of the quote at the bottom of the license plate.
None of the people I talked to in DC had a clue why this was on all of their license plates.
My cousin, upon hearing this quote (and its omission), laughed... and then didn't believe it... and then looked sad and said "yeah."
After actually reading the Wikipedia page that I just linked, the omission is deliberate and has specific origins.
The District of Columbia (DC) pays Federal taxes but doesn't have representation at the Federal level. The DMV in DC added this to the license plates that it printed to acknowledge that, and to protest it.
So, literally, people in DC feel that they pay Federal taxes without representation. That's what that's about... rather than a blunt nod towards power imbalance, or something silly like that.