This seems like a simple system - it is if you know the rules
1) Keep the wheels aligned straight
2) Put gear in neutral position
3) Do not lock the hand-break
One may ask why?
The car parks are not only the designated parking spaces. You are able to park your car at right angles behind parked cars IF you follow the above rules. This will enable the car park attendants to push the cars backwards or forwards to be able to increase the possible amount of parking spaces.
BUT if you do not follow the rules I am not sure what happens - I have seen this car towed away but I am not sure how you can get your car back and how much it costs...