I'd say the state, same as the handicapped plates/placards. Doctors letter and you get a free small ID card. I'm not saying they should wear a flava flav clock around their neck saying they have a disability, or that the dog should even have to wear a vest.

If anything it would make things easier and protect privacy since it would eliminate the need to ask the question "what task has the dog been trained to perform" Which seems to all but out what disability the person has.

I am sorry that I never saw this thread. It is a bit dated, but if I can be of any assistance now, please let me know.