In my opinion, the sign is ambiguous. It makes no mention of people not staying at the hotel hsving to pay for parking. ergo, Contra Preferentum should apply.
https://en.wikipedia.org/wiki/Contra_proferentem
This is an entirely unregulated industry which is scamming the public with inflated claims for minor breaches of contracts for alleged parking offences, aided and abetted by a handful of low-rent solicitors.
Parking Eye, CPM, Smart, and another company have already been named and shamed, as has Gladstones Solicitors, and BW Legal, (these two law firms take hundreds of these cases to court each year). They lose most of them, and have been reported to the regulatory authority by an M.P. for unprofessional conduct
Hospital car parks and residential complex tickets have been especially mentioned.
The problem has become so rampant that MPs have agreed to enact a Bill to regulate these scammers. Watch the video of the Second Reading in the HofC recently.
http://parliamentlive.tv/event/index/2f0384f2-eba5-4fff-ab07-cf24b6a22918?in=12:49:41
and complain in the most robust terms to your MP. With a fair wind they will be out of business by Christmas.
You never know how far you can go until you go too far.