There are many reasons why a dog may need space:
Health issues,
they’re in training,
they’re being rehabilitated,
they’re scared,
or they are reactive around other dogs.
If you see a dog with a yellow ribbon or something yellow on the leash, this is a dog who needs some space. Do not approach this dog with your dog. Please maintain distance or give this dog and his or her person time to move out of your way.
Source: FB/The Yellow Dog Project