No, your service dog is not required to wear a vest, patch, harness, or any form of identification under federal law.
According to the U.S. Department of Justice's official guidance on the Americans with Disabilities Act (ADA):
Service animals (primarily dogs) are not required to wear a vest, ID tag, or special harness.
Businesses and public entities cannot require documentation, certification, registration, or proof that the dog has been trained or licensed.
Staff may only ask two questions if it's not obvious that the dog is a service animal: (1) Is the dog a service animal required because of a disability? and (2) What work or task has the dog been trained to perform?
Why many handlers choose to use vests anyway (optional but recommended by many):
Clearly signals to the public and staff that the dog is working, reducing questions, petting attempts, or access challenges.
Can include patches like "Do Not Pet" or "Service Dog" for better visibility.
May carry useful items (e.g., medical info in pockets).
The QR code on your ID tag or card allows immediate verification, making it easy to access your legitimate letter without delays or unnecessary searching.