Almarg
Re "IDDOC," Plato also had it right in his post above. To be sure it's clear, the holder of the license plate would be a doctor who deals with problems involving the id. In other words, a psychiatrist. The relevance of "Forbidden Planet" is that someone who remembers that scene knows what the id is :-)
I was not trying to leave anyone out, posts here dont always appear in the order they were sent.
Als was the first I read and I was surprised anyone got it so quick. Other replies, Infectious Disease and Illegal ID are appropriate but I like to think the personal plate was inspired by Forbidden Planet.
Im a huge fan of Forbidden Planet. Its in good company with only a couple of other Sci Fi movies that qualify as best ever (on my list).
Loved the original 1956, Invasion of The Body Snatchers and original 1951 version of The Day The Earth Stood Still.