This is scary. The SSN is abused similarly.
It's not uncommon for a financial institution to ask for "the last four digits of your social" to authenticate your identity. The thinking apparently is that if you know those four digits, then that's proof that you are who you say you are.
But not very long ago the SSN was used widely, mindlessly and indescriminately for everything from driver's licences to miltary service numbers to college IDs to insurance policy IDs. We were even encouraged to inscribe it on our belongings so the police could return them to us if they were stolen and recovered. One video rental where I rented movies long ago even required your SSN to rent a movie.
And as late as last year, a ski rental shop where I rented skis had a blank on the rental form for your SSN. My friends and I never fill it in, of course, but I'm sure some people do.