A service dog, by definition, performs a service for the owner (or handler, depending on which terminology you want to use) that the individual would otherwise not be able to accomplish on his or her own as a result of a disability. A service dog is hopefully of steady temperament and a good working drive. A service dog has been extensively trained and behaves appropriately while "on duty".
Here's the ringer, however: is there a nationally recognized certification for service dogs?
Because the ADA requires service dogs to be granted access to public spaces where dogs might not otherwise be allowed, it seems as though there would be some sort of national certification. Indeed, individuals with service dogs (I keep saying "dogs" because the ADA changed the law last year, making service animals dogs only, referenced here: How was the definition of service animal changed?) need not carry documentation of their particular disability to present as proof that their dog is necessary.
A service dog must have appropriate behavior or a business owner may ask that person to remove their dog (referenced here on the ADA site) and that really seems to be the best rule of thumb for whether an animal is an appropriately trained service dog.
Of course, there are programs who train dogs and match them with people. Guiding Eyes for the Blind is one, and The Delta Society is another, which deals with both service dogs and therapy dogs. Pretty much everybody's heard of a Guide Dog; have you heard of a Seizure Alert dog? An Autism Dog? A PTSD Dog What about a Migraine Alert Dog?
If somebody has an "invisible disability" and a service dog, they are granted the same rights as somebody with an "obvious disability". A manager at a business can make sure that your dog provides a service; he or she cannot ask what your disability is, or at least they shouldn't.
Service dogs are working dogs, which interests me immensely. Dogs performing tasks is a fascinating thing to me, as I've mentioned before. I started this post declaring that Elka is not a service dog, though perhaps one day she could be. I get migraine headaches, a thing which can be debilitating and very limiting. I'm pretty well off, really, as I don't necessarily have a headache every day, much less a full-blown migraine. And I've gotten fewer full-blown migraines since we got Elka.
I'm part of the percentage of migraine sufferers who have a distinct "aura phase", before I ever have any pain at all from the headache. If I take painkillers during this phase, my migraine will be severely diminished, if it doesn't go away in its entirety. Elka knows somehow to alert me during this stage. It's an unpolished, spontaneous (i.e., I didn't teach it) behavior at this point: she'll stare at me, whine, not leave me alone. Unfortunately, this sort of behavior can be par for the course in everyday life, but I've been working on listening to the dog more, and trying to discern the causes of her whines. And sometimes, those whines mean I'm headed for Headache Land pretty quickly. You can bet I reward her for that! Given the commands the already knows, I could also teach her to bring me a bottle of painkillers and a bottle of water at times like that (though I don't want to teach her how to open the fridge...she'd never want to close it!) I could teach her how to turn off the lights in the room where I go to lay down (I get extremely photosensitive). She will already brace to support me if my balance isn't so great.
However, as you may have gleaned from prior posts on our training sessions, Elka would not currently pass a public access test, were I to go through the one that the Delta Society provides. She is very friendly, but also still very young and interested and excited about the world around her. She still gets startled by things, and focuses on things other than me. Could she be trained? Yes. Will I ever use her in that capacity? Probably not. My migraines aren't debilitating enough that I consider myself "disabled"; I miss work because of them, but not enough that I might as well just stay home.
Some people hear all of this information (about service dogs in general, not the Elka-specific stuff) and think "well gee, I can just put a vest on my dog and take it everywhere with me!" And some people actually do that. Which is illegal, as you may have noticed, and is also unethical. Having one's not-trained, ill-suited, not-service-dog out and about masquerading as a service dog makes it easier for legitimate teams to be taken less seriously. It builds a case for limiting access that people with disabilities and real service dogs genuinely need. Can a person train his or her own service dog, rather than going through an organization? Yes. Should they try to be as thorough in that dog's training? Definitely.
So, in closing, service dogs are rad and provide an independence and quality of life for people who might otherwise be rather limited. Also, don't pretend your dog is a service dog if he or she is not, because that just ruins it for the people who need it.