Federal Law 36.302 of the Americans with Disabilities Act guarantees access rights to all public places for people with assistance dogs which includes guide dogs, service dogs (dogs that help someone who uses a wheelchair or walker) and hearing dogs.
Some states have their own laws - for example: Maryland State Law Articles 30 and 33 guarantees access rights to all public places for people with assistance dogs - including guide dogs, service dogs (dogs that help someone who uses a wheelchair or walker) and hearing dogs. In addition, the MD law requires hearing dogs to wear a bright orange leash and collar when out in public as identification. No "badge" ID is required. Check to see if your state has a similar law.
A great resource is the one-page ADA Brief on Assistance Dogs in Public Places. You may find it to be very helpful when confronted by business managers/owners. Carry copies of it with you at all times and leave it with anyone you think needs to understand it. Also encourage business managers/owners to share the document with their employees so that (just maybe) you won't have the same problem the next time you visit their place of business.
The following is part of a regular pep-talk given at a hearing dog training school in Maryland to new hearing dog owners before they venture out for the first time with their assistance dog: "Please keep in mind that wherever you go, you and your dog will be representing all assistance dog teams. Your behavior in public as a team will ultimately reflect on us all - negatively or positively - and will influence how people perceive assistance dogs."