My all-time favorite was a Maryland plate on a gold Corvette that regularly parked in the Pentagon's north parking lot, because I wondered just how in hell he got it past the censors: "TWT LVR".
And this was long before Twitter even existed...
I saw a Maryland plate at a dry cleaners in Catonsville that said “cptmchr”. Based on the occupants I am 100% sure what it meant. Still mad I didn’t get a picture of it.