vessel shall not be required to be numbered under this
Act if it is:
(1) Covered by a certificate of number in full force and effect which has been issued to it pursuant to Federal Law or a federally approved numbering system of the United States provided that such vessel shall not be used on the waters of this Territory for a period in excess of sixty (60) consecutive days.

10 Guam Code Ann. HEALTH AND SAFETY
CH. 69 BOATING

(2) From a country other than the United States, provided that such vessel shall not be used on the waters of this Territory for a period in excess of sixty (60) consecutive days.
(3) A vessel whose owner is the United States, a state or a subdivision thereof, used exclusively in the public service and which is clearly identifiable as such.
(4) A vessel’s lifeboat if the boat is used solely for lifesaving purposes. This exemption does not include dinghies, tenders, speedboats, of other types of craft carried aboard vessels and used for other than lifesaving purposes.

(5) A vessel belonging to a class of boats which has been exempted from numbering by the Guam Police Department after said Department has found that (1) the numbering of such class will not materially aid in their identification and (2) an agency of the Federal government has a numbering system applicable to the class of vessels to which the vessel in questions belongs, or (3) the vessel would also be exempt from numbering if it were subject to the Federal law.
(6) Documented by the United States Coast Guard or a
Federal agency successor thereto.

(7) When operating temporarily by virtue of evidence that a recent application for a certificate of number has been submitted.
SOURCE: GC § 8995.4.