Doc. Numbers
According to regulations, you have several choices. One of the most common is to put you documentation numbers on a board and mount is securely in the boat. While this has been accepted by the Coast Guard, the questions surrounding the removal of the board is a tough one to answer. I have mounted my documentation numbers on my last 3 boats in one of the storage area under the setees. You can buy the numbers at any marine store, mount them right on the hull and then buy some fiberglass resin and cover the letters with several coats of resin. I would suggest taping off the area since the resin is very thin an can run on the slanted surface. This will make for a very neat installation, just make sure you pull the tape off before the resin is set or you will have the tape included. It will look very professional and will meet the Coast Guard requirements.