Spotted on a recent P&O Cruise, one of the fanciest door decorations.
We all know that your steward will add a card (or similar) to your door on your birthday or if you are celebrating anything (hint: you may have to let you stewart know a few days in advance).
However most cruise ships will also let you add a few decoration to your door if you are celebrating anything. Please remember to use blue tack (so as not to damage the door or wall) and light weight hangings (paper, streamers, etc). If in doubt, just ask you room steward before hanging anything.
These may be cleared away by your steward after a day or two. Have fun on your cruise.