To be in compliance with the USCG, a documented vessel must be marked properly.
Specifically, “NO.” (“N” and “O” followed by a period) must be marked before the vessel’s assigned official number. This must be marked in Arabic numerals that are at least three inches high and in block type. Additionally, these must be placed on some interior structural part of the hull where they’ll be clearly visible and, they must be permanently affixed. In terms of “clearly visible,” use common sense.
In this context, “permanently affixed” means that altering them, removing them, or replacing them, would not only be obvious, but it would also cause damage, scarring, or the like to the surrounding area.
A commercial vessel’s name must be marked on the port and starboard bow. Additionally, a commercial vessel’s name and hailing port must be marked on the stern as well.
A recreational vessel’s name and hailing port must be marked together on an exterior part of the hull that’s clearly visible. Again, use common sense.
These markings can be made of any means and materials, so long as they are at least four inches in height, durable, and clearly legible. Of course, they must be of Arabic or Roman numerals as well as letters of the Latin alphabet. When marking the Hailing Port, the place, as well as an (abbreviated) State, Territory, or possession of the United States, must be marked as well.
Subpart I covers marketing requirements for vessel documentation.