A cape, jacket, or vest is an article worn by a working dog to identify or assist them in their job.
Many assistance dogs wear capes if nothing else than identification is needed. They often bear the logo of the organization that trained them, the names of companies that sponsored their training, and usually a patch requesting that the dog is not petted or distracted. Although they are not assistance dogs in the legal sense, some therapy dogs wear similar capes to identify them as such.
A police or detection dog might wear a jacket to identify them and/or protect their torso. Some short-haired or less hardy dogs wear jackets when it is cold, much like a human does.
Another piece of equipment similar to a cape is the harnesses that guide dogs and some mobility assistance dogs wear for leading, bracing, or pulling. Also, assistance dogs that carry items for their handlers wear backpacks, though sometimes these are also referred to as jackets.