Flood defences

I drove past this in the car today but had to go back on foot to check I had read this sign correctly. I'm not at all sure whether the instruction 'do not remove' is intended to refer to the wall or the sign itself. However, in view of the damage that can be caused by flooding I sincerely hope that nobody would be tempted to sneak up and remove the wall. Wall thefts and removals as we know are commonplace these days and I hope this warning notice serves its purpose and deters any potential culprits.