I think there is often a grey area at such objects within which the decisions of others should be respected. 
The sign could be the same one as at https://www.openstreetmap.org/note/4094704 so please have a look at https://commons.wikimedia.org/wiki/File:Spielplatz-wilhelm-heinrich-bruecke.jpg (uploaded only for these notes :), it was really hard work with wrong language for the description too).