There's a tag on the inside of your cabin door for as long as I can remember 20 plus years.
On the Nieuw Statendam it reads Tidy up Please, We put it on the front of our cabin door when we need service.
It works Excellent and makes it easier for the room stewards.
We are on the Nieuw Statendam , which is a full ship. Staff is friendly, We had dinner last night in Canaletto which was excellent.
Music Walk is hopping every evening.
I am impressed.