Requirements for valid disabled parking spot

My oul fella is tipping 80, and for health reasons would be entitled to a disabled parking spot. However, for reasons best known to himself, he refuses to do the application.

He got a parking fine recently for parking in a disabled on-street parking spot in town. The spot was put in front of a doctor's surgery which has not operated as a doctor's surgery in years. He insists that it's not a valid disabled spot as there's no street sign as required by law, and that he would never park in a disabled spot. I wasn't able to find anything to state that a sign was a requirement for a disabled spot to be "valid". The spot definitely does still has the white wheelchair symbol in white paint, but it's faded and so old that it never had the blue paint job done. Can anybody set the record straight on whether he needs to take his medicine or has grounds for an appeal.