Serenade of the Seas question

We will be on Serenade with friends who will be celebrating their 50th anniversary. I would like to decorate their cabin door and was wondering if anyone knows if the doors are metal and will accept magnets. If not, any suggestions what to use to put up a cardboard sign? (Not sure about using tape on the door.) I don't want to purchase the RCCL anniversary gift packet as I do not think they would care for the room decorations.

We will be on Serenade with friends who will be celebrating their 50th anniversary. I would like to decorate their cabin door and was wondering if anyone knows if the doors are metal and will accept magnets. If not, any suggestions what to use to put up a cardboard sign? (Not sure about using tape on the door.) I don't want to purchase the RCCL anniversary gift packet as I do not think they would care for the room decorations.

The doors are metal.

All metal. As are the walls. :)