I understand why we need some of these signs. Some are up for safety reasons or they explain rules or laws for example. Others set a policy that makes things go smoother or explains how something should be done.
You've seen them and, being unaware of this law as I was, probably didn't even bat an eyelash. Although, you may have raised an eyebrow. They are blatant about it, almost intentionally trying to draw attention to their flagrant lawlessness.