33 C.F.R. § 173.33
Removal of number
The person whose name appears on a certificate of number as the owner of a vessel shall remove the number and validation sticker from the vessel when:
(a) The vessel is documented by the Coast Guard;
(b) The certificate of number is invalid under paragraph (c) of § 173.77; or
(c) The vessel is no longer principally operated in the State where the certificate was issued.