What's P'shat? III

This morning as I walked to work, I noticed a cab with a decal that said, "Working Dogs Welcome".

Working dogs, it turns out, is PC for 'seeing-eye' dogs. My first thought was, if you are going to go PC, shouldn't you go all the way? Shouldn't the sign have read, "Working Canine American's Welcome"? But then I realized that might cause a ruckus with French poodles and German Shepards. But we digress.

My main question is, who, exactly, is going to read the sign on the cab? A blind person walking with his or her 'working dog' certainly can't read it and although I understand seeing-eye dogs are amazingly well trained, I don't think they've been trained to read. I could be wrong.

So, what's up with the sign?