The owner or anyone with a contract for the space, can remove a car at any time, however they are open to a claim for damages physical and civil in doing so. As they cannot tow it away, leaving in another space or area may put them in breach of the lease.They certainly cannot destroy it or have the LA destroy it except where the right circumstances apply.
If it ain't yours, don't park in it. If the space is your then subject to the terms on which you occupy or own the space consider erecting a simple post/barrier.
Based on the information posted, I offer my thoughts.Any action you then take is your liability. While commending individual effort, there is no substitute for a thorough review of documents and facts by paid for professional advisers. More ramblings atleaseholdpropertymanager.blogspot.com