To be honest, it's arguably easier to make a signage argument in the first person anyway, walking the assessor through the route you took, and the lack of any signage between entering the site and parking.
You can almost present the images as a photographic 'walk/drive through' recreation.
When you're going getting photos of the entrance, it may also be worth having a hunt around the entire area for any signs that are there, even if they're nowhere near where the driver parked. That way you can pull together a map/signage diagram, that you can use to pre-emptively refute any claims from CPM that there is additional signage. It's not unknown for signage to have fallen down/been removed, and the operator not to have updated their signage plan.
