Based on Ja zuster, nee zuster (1966), a hugely popular TV series of which very little footage remains, as most episodes were taped over in order to recycle the expensive tapes that they were filmed on.
The red cross on the men's singlets has the letters J, Z, N and Z in the four corners. These are the initials of the film's title. The red cross on the marching girls' costumes is surrounded by the name of the film.