Service dogs and emotional support dogs are not to be confused with each other. A service dog is covered under ADA, trained and sometimes wears clothing identifying it as such (not required). Because a service dog is considered to be medical aid, you cannot discriminate a person with one. An emotional support is a dog that does not necessarily have any particular training and is simply available for comfort. I am aware of people providing letter from their therapist supporting the dog, but the dog is not a necessity.