We humans are magnificent creatures! So adaptable because we're capable of applying our hard-won experience to new situations. So even if we're seeing something for the first time we will not be overly surprised if we have a frame of reference established. In everyday situations we use this all the time. It is as we say simply common sense. But apparently some people don't think a lot before acting, thus prompting concerned sign makers to stress the obvious. And some of those examples can leave us helpless with laughter.