They are becoming increasingly popular. We use to only see one or two but during the last couple of cruises we've seen several more. Go for it! It makes your cabin much easier to find - which is a good thing since your sail and sign card (door key) doesn't have your cabin number on it!
We always decorate our door too. Being from Florida we have a cardboard palm tree and also use little flamingos, dancing people, etc on the door. We put them up with the sticky putty you can get almost anywhere including Walmart. Lately I have been downloading a picture of our ship and printing it on regular paper along with the ship hame, our first names and hometown. Does make easy to find your cabin.
Dawn Princess -