I was on a steam excursion in Copenhagen last weekend and saw this. The coaches were 1940s stock used on suburban services into the 1970s (most of these lines are now modern electrified near-metro routes).The toilets are water flushed bottom dump, and we were using them. The sign says that the toilets will be locked essentially within a 25 km. radius of the city center (roughly where the most residential housing is close to the tracks). No one bothered to lock/unlock the toilets on this single roundtrip.
Interesting side note: the trucks on these coaches have wooden frames, as a wartime materials shortage measure.