And it prevents people from accidentally barging in because suddenly your door doesn't look like their door. We had a next-door neighbor on our first voyage who walked in several times without knocking, thinking our cabin was his cabin. Luckily we were dressed! Eventually we started locking the door when we were home.
The cabin doors are steel clad with thin (fake?) wood veneer. SAS provides you with a couple of strong magnets to attach name tags to the door. You MAY NOT tape anything to the door, but you are free to use your own magnets or sticky notes that leave no residue. Lots of people do this, and it's fun!
A lot of the students have sticky notes that show where they can be found: Home (knock!), Lido, Library, Pool Deck, Gym, Class, etc. They pin the magnet to the right sticky note so their friends can find them.
I recommend bringing a set of those very strong little magnets for your door decor. You can keep your eye on little items in each country that would look great on your door. Many touristy places sell kitschy fridge magnets that will spice up your cabin door. Jennifer even brought special door items for each holiday.
On our last voyage we brought a tiny portable photo printer and printed selected pics from each country to magnet to the door. By the end of the voyage it was like a bulletin board collage of our semester.
