We place minimal magnets on our concierge doors on the wood veneer paneling. We usually have one or two smaller signs, and use the strong rare earth magnets so that they stay up. We've always found that at least one small sign gives us a little sense of ownership for the time we're on board, and also makes it handy for children to find the correct room. The wood work is beautiful, but many people still find at least a small way to personalize. As a note, the doors on the classic ships have been re-painted so many times that it's also handy to have those super-strength magnets for decorations. Have a wonderful cruise!