The sign giving the parking conditions is right by your car, but the suspension sign would seem to have slipped down the pole, so is obscured by the green cabinet which I assume is for telephone cables. So it is not prominent at all.
So I suggest you submit an informal challenge based on your narrative, pointing out that as a BB holder you do not have to walk to the ticket machine, and on exiting the car, saw no suspension sign. The sign was found after you returned to the car and found the PCN, which was at the bottom of the parking sign pole, and thus invisible to anybody on the other side of the roadside green telecoms cabinet. Don't be confrontational or anything at this stage.