Actually, if I had to guess, I'd say it is a backwards compatability issue and/or a really old machine. Making a machine that can "read" braille isn't hard. Does the card for blind drivers have "do not fold, bend, spidle or mutilate" on it? If it goes back more than 20 years, odds are it has a series of pins that are tied to a mechanical computer that detemines how much is owed, or at least did at one point. I bet the designer decided to go with braille, becuase it is a universally standardized set of characters, you could get the imprinter as an off the shelf item or very nearly so.

Or if it is read by a human attendant, it might be there for a blind attendant. The blind need jobs to, and a job where you sit in a booth is pretty safe, nothing to trip over.