The only location stuff I could ever remember was DL for the Isle of Wight.
Spain had a similar system of displaying where the car was registered. The middle letter would be the city of origin - M for Madrid, B for Barcelona, etc. They just recently scrapped this system as cars on an 'M' plate would often find themselves vandalised if parked in Barca and vice versa.
I don't think our city rivalries quite extend that far - you just have to remember to never visit Liverpool and you're done