It's New York license plate reads "M7F 540".
While cleaning out the car and getting ready to sell it, Frank found a pair of Ray's old swimming trunks. And in the pocket of the trunks was Ray's old fake ID.
Ray used to borrow the car a lot when he was in school. While on a date with Lisa, Ray ended up having sex with her in that car. So then Ray nicknamed the car "Lucky".
In the present day, Ray wanted to buy the car from his father. And it broke down while Debra was at the supermarket with the kids. So, Ray began fixing it up, not only to keep it running, but also to preserve his memories of it.