It has one sign as you drive in on the left but no further ones on that side.
From the images taken of the car as shown on the PCN, it appears that it was parked directly underneath a sign, so I think it would be a challenge to argue that the signage wasn't sufficiently visible. But the reason for issue being listed as 'No Permit' suggests that there could be an argument that the signage is forbidding - can we see a photo of the signage?
appeal as RK and not being driver
From a quick look they appear to have complied with Schedule 4 of the Protection of Freedoms Act (PoFA), so not being the driver would not help, as they appear to have met the conditions to hold the keeper liable.