license number
registration number

If nobody got the license number, he was home free.

I wrote down the license number and went back into the station.

"But how do I know this isn't just some license number you had already?"

He walked behind it and wrote down the license number.

If she got their license numbers, the police could check them out, at least.

If only she could have seen him full face or caught the license number of his car!

I got the license number of the car that followed me today.

"She even took down the license number of the car."

If only he could think of a way to change the license number.

Somebody took his license number and the police were called.