A pond named "Schlossgartensee" in the Schlossgarden of Stuttgart, the Sign says "Keep off the Ice!" ;)
<a href="//commons.wikimedia.org/wiki/User:Stefan-Xp" title="User:Stefan-Xp">Stefan-Xp</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>