WHO 1

WHO1 was Bessie's original number plate. (TV: Doctor Who and the Silurians) It was later changed to WHO7. (TV: Battlefield) and then, further, to WHO 8. (PROSE: The Dying Days)

The yellow roadster's plate again read WHO 1 after the Eleventh Doctor transformed it into a monster truck. (COMIC: What He Wants...)

Behind the scenes
The WHO 1 number plate was originally taken, so it could only be used on private grounds, and never on the road.