Walking through a park near Frankfurt, Germany I saw this sign. Checking first to make sure I had not slipped back in time to the 1880s, I snapped this photo. What does it mean? Not reading German, the only way this visual control could have been any use to me is if I had seen it while riding my penny-farthing. Alas, it does not fit into my suitcase. A highly situational, and therefore largely ambiguous, visual control.