"Bicycles will be removed" - legal?

there is a concept in english law called distress damage feasant - the extent to which this would apply to bikes chained to private railings (or other private property) is as far as I can tell unknown and presumably has not been tested in the courts.
if it helps, the idea is as follows:

if you dump your bike on my land you are trespassing on my property (unlawful - nb in the civil context). various remedies are available to me. I can sue you for trespass to property in the hope of recovering damages from you proportionate to the harm your trespass has caused (which is going to be a lengthy, costly and generally annoying process) - or i can simply detain the offending bike until such damages as have been caused are paid to me by you.

so far so good, although it should be noted that in order to rely on this remedy (and not be liable in turn for taking the bike) I would have to be able to show that some damage was caused (this doesnt have to be physical damage, but has to amount to more than the distress of the bike's presence alone) - exactly what would be acceptable damage in this context is unclear as far as i can tell...

furthermore, removing and detaining the bike in most cases would involve breaking whatever lock was in place - again, its unclear whether the self help remedy outlined above would allow someone to do this lawfully.

This issue has been most considered in the context of car clamping and i think its likely that if the issue re bikes did go before the courts, it would be considered analogous or close to that, although not without difficulty.
cars can be lawfully clamped and released after payment when trespassing on private property, but subject to various restrictions (notices, regulation of operators etc) (if interested see the case of Arthur v Anker) none of this i think applies to bikes however, and doesnt envisage bike specific issues such as damage to locks for example.

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.

the situation might well differ where you lock your bike to public property as the rules applying to local authorities are perhaps different.