A really quite disgraceful placement of the sign controlling the bay, but whether this would win at an adjudication is another matter. The bay does have the text "Loading Only" on the carriageway by the bay, and a motorist parking in any marked out bay has a duty to look for the sign controlling the bay. But would this motorist look for a sign that sits almost out of sight below the street name ?
Is there any background info on why your father parked there ? In order to give full advice we need to be in possession of all the facts.