At the Pet Expo the other day I saw a dog walking around with a collar and lead that said 'blind dog' and I automatically moved aside to give him and his human plenty of room.
Later I came across this dog sitting on one of the stands.
Okaayy... so he's friendly. Does that mean that when he's out and about, everyone should pat him? I think that might be the reaction of the public to seeing such labelling of his personality. I wouldn't want to take Penny walking in a harness like that.
On the other hand, at training it could be useful, because when she's 'working', she focuses closely on me and really doesn't like it if other dogs come within her workspace (ie within a few metres of her and me). She might benefit from the harness labelled 'no dogs'.
I can see a role for these types of harnesses, but I have my reservations.