That's not what I said. Dogs simply are not required to wear vests.
Then how would someone know that a service dog is a service dog?
Most people do not know that there is a big difference between a service dog and a therapy dog, although service dogs can be therapy dogs for the handicapped person.
People are not supposed to approach service dogs, and are not supposed to try to pet them. The advantage of having a service dog vest with the proper patches is that one patch says “Please do not pet me, I am working”
Owners of service dogs can carry cards to hand to others explaining that the dog is working, and to leave them alone. This would be very helpful to people like my husband, who is losing vocal cord control, and is now very hard to hear and understand.