I remember reading a thread about Princess ship passengers decorating their doors. At least two people had gripes about their cabin stewards saying there is a rule against it. The reason they did not want paper on the door was the fire risk, so I thought if I have a sheet of magnetic paper instead of four small magnets holiding it up, I should be OK.
My mom is terrible in the finding directions department. However the main reason I will stick a magnet to it is it adds a fun element to the cruise. Why not since Carnival calls its fleet the fun ships? And for my first cruise ever, it is nice to have something marking the occasion.