This is where I recently got my info. on the USCG documentation lettering. (To avoid further confusion, NO state requirements are included in this post.)
COPIED FROM USCG SITE:
The name and hailing port of a recreational vessel must be marked together on some clearly visible exterior part of the hull. The vessel name of a commercial vessel must also be marked on the port and starboard bow and the vessel name and the hailing port must also be marked on the stern. All markings may be made by any means and materials that result in durable markings and must be at least four inches in height, made in clearly legible letters of the Latin alphabet or Arabic or Roman numerals. The "hailing port" must include both a place and a State, Territory, or possession of in the United States. The state may be abbreviated.
The official number assigned to documented vessels, preceded by the abbreviation "NO." must be marked in block-type Arabic numerals at least three inches high on some clearly visible interior structural part of the hull. The number must be permanently affixed so that alteration, removal, or replacement would be obvious and cause some scarring or damage to the surrounding hull area.
COPIED FROM BOATUS SITE:
Federally Documented Vessel Requirements
Character Requirements:
• Can be made by the use of any means and materials which result in durable markings.
• The application for documentation must include a name for the vessel composed of letters of the Latin alphabet or Arabic or Roman numerals and may not exceed 33 characters. The name may not be identical, actually or phonetically, to any word or words used to solicit assistance at sea; may not contain or be phonetically identical to obscene, indecent, or profane language, or to racial or ethnic epithets.
• Must not be less than four (4) inches in height (all characters).
• Can be on the transom or either side of the vessel.
• The vessel must have the official number permanently affixed in block-type Arabic numerals of not less than 3 inches in height, preceded by the letters “NO .” on some clearly visible interior integral structural part of the vessel.
• The "hailing port" must include a place and a State, Territory, or possession of in the United States. The state may be abbreviated.
• Note: There is no requirement for block letters or any other restrictions to type, font, or color for federally documented vessels.
Placement & Additional Requirements:
• The name and hailing port of a recreational vessel must be marked together on some clearly visible exterior part of the hull.
• Many recreational vessels will place the vessel name and hailing port on the stern, and vessel name on both sides of the bow, which is required for a commercial vessel. Although not required for a recreational vessel, this is an acceptable option.
• The above requirement for vessel name and hailing port to be CLEARLY VISIBLE may necessitate duplicating the name and hailing port on either side of the hull.
• When dinghy’s are stored on the swim platform or transom causing the Vessel's name and hailing port to be obscured from view, there is no Federal requirement to place the name and hailing port elsewhere. That is a Law Enforcement issue only.
• Stenciling on the bottom of the dinghy is not considered a permanent marking.
• Federal Vessel Documentation is a federal issue and is not open to enforcement or interpretation by the state.