"Bicycles will be removed" - legal?

I think this is probably the practical point here...

all i can reasonably say is that if someone has gone to the trouble of putting up a threatening sign, they might care about it enough to break your lock and take your bike / and it would then be for you to take action to get it back and recover any damages for the lock. given that the law is uncertain, it would unlikly be a straighforward process, and litigation of any sort is inevitably costly, worrysome and inherently risky. for those reasons alone, and perhaps thinking simpy that you would not care for a random to chain their property to yours and bugger off, it might be best to avoid locking your bike to private property.

I would guess that whoever takes a bike in this case would not surrender it easily. You could probably bet that they will make it difficult to contact them or deny responsibility at the outset (unless they are looking to gain a quick buck)...