It may be beneficial if the recipient of the notice posts directly, as it can occasionally turn into a game of Chinese whispers otherwise, and they are the one who is going to need to submit any appeals, or legal defences if it goes that far.
Another thing to note, so that they are going into this with their eyes open, is that regardless of the strength of any appeals, VCS are likely to reject them, as are the 'Independent Appeals Service'. VCS can be litigious, so if they're going to fight this, your guest may need to be prepared to defend themselves in the County Court (Small Claims track).
It would be helpful to see a copy of the notice they have received.
One point to note is that the signage looks 'forbidding' - there's no consideration offered to the driver, only to those in possession of a permit, so one could argue that no contract was formed.
