Rene Grohnert and I are collecting pictures of signs that attempt to forbid posting, like "Plakate ankleben verboten" in german, "defense d'afficher" in french or "no anunciar" in spanish. This particular example comes from my recent trip to Hong Kong.
If you have more examples, we would appreciate if you could send them to me ( wanner(at)datacomm.ch ), maybe we can make a web exhibition some day.