Just off the top of my head I can only think of 2 answers.

About Car 51 in the television show.

and Area 51 out in New Mexico.

Just guesses
geonagual Reviewed by geonagual on . Pink Floyd Trivia Question Two things just happened to come together this weekend and I thought "holy shit, that's were that came from" Back in 1970, Pink Floyd did a soundtrack to a film called Zabriskie Point. One of the songs on that soundtrack is called "Come in number 51, your time is up" A weird name for a weird song. Question is, where did they get that name?? Rating: 5