Service animals help people with a variety of disabilities, some of which might not be visible. There is no requirement that a service animal wear a tag, be registered, or display any kind of proof that it is a service animal.
Some regulations provide that you may ask two questions to confirm that a rider's animal is a service animal:
1. Is the animal required because of a disability?
2. What work or task has the animal been trained to perform?
You may not request that the rider present documentation proving that the rider's animal is a service animal.