50 CFR § 660.20 - Vessel and gear identification.
(a) Vessel identification -
(1) Display. The operator of a vessel that is over 25 ft (7.6 m) in length and is engaged in commercial fishing for groundfish must display the vessel's official number on the port and starboard sides of the deckhouse or hull, and on a weather deck so as to be visible from above. The number must contrast with the background and be in block Arabic numerals at least 18 inches (45.7 cm) high for vessels over 65 ft (19.8 m) long and at least 10 inches (25.4 cm) high for vessels between 25 and 65 ft (7.6 and 19.8 m) in length. The length of a vessel for purposes of this section is the length set forth in USCG records or in state records, if no USCG record exists.
(2) Maintenance of numbers. The operator of a vessel engaged in commercial fishing for groundfish must keep the identifying markings required by paragraph (a)(1) of this section clearly legible and in good repair, and must ensure that no part of the vessel, its rigging, or its fishing gear obstructs the view of the official number from an enforcement vessel or aircraft.
(3) Commercial passenger vessels. This section does not apply to vessels carrying fishing parties on a per-capita basis or by charter.
(b) Gear identification. Gear identification requirements specific to fisheries using fixed gear (limited entry and open access) are described at § 660.219, subpart E and § 660.319, subpart F.