Yellowdog is a means of promoting awareness generally and signifying to other dog owners that your dog is not happy around other dogs. It may be that your dog is recovering from an illness or operation, or is nervous around other dogs, or insecure, or in training, or unwell, or just old and tired. If you see a dog with a YELLOW ribbon, bandanna or similar on the leash or on the dog, this is a dog which needs some space. Please, do not approach this dog or its people with your dog. They are indicating that their dog cannot be close to other dogs.
Brilliant idea! Good luck with your campaign.