most of the big chain hotels are heading this way, especially those near shopping centres or motorway junctions (they get used as park-and-rides by lift sharers)
In a lot of cases the warning signs are inadequate anyway - I got an invoice in the post for £100 for parking at one hotel one evening. I went back and checked: the signs stipulated a charge of £80, not £100 and 18 of the 20 warning signs were attached to faulty street lamps and could not be read in the dark at the height they'd been set at. Besides which the vehicle registration input machine was hidden behind a sign.
Over the next 12 months I got a lot of threatening letters, but ignored them all, sat back and awaited the court summons. It never came, they must have known they'd get destroyed in court because the invoice was for the wrong value and the signs were illegible. Time has expired now, so I won.
So, to Holiday Inn and Parking Eye, if you're reading this FUCK YOU