what are those numbers in the back windows of cars?

Question

have you ever seen the number in a red square in the back window of a car?it's usually on older cars...whats that number meen?

Answer 1

They are a permit given by the dmv because there is some problem that caused them to not be able to renew the registration. The number is the month that the permit is for.

Answer 2

Now days the stamps are made into either a bar-code for really modern cars(2003-current) or numbers for the older cars(1987-2003). The numbers in the red box are there to tell the repair shop as well as the police and insurance companies where the glass was made as well as the date of manufacture of the glass.