17 U.S.C. § 204

1. (a)A transfer of copyright ownership, other than by operation of law, is not valid unless an instrument of conveyance, or a note or memorandum of the transfer, is in writing and signed by the owner of the rights conveyed or such owner’s duly authorized agent.
2. (b)A certificate of acknowledgement is not required for the validity of a transfer, but is prima facie evidence of the execution of the transfer if—
   1. (1)in the case of a transfer executed in the United States, the certificate is issued by a person authorized to administer oaths within the United States; or
   2. (2)in the case of a transfer executed in a foreign country, the certificate is issued by a diplomatic or consular officer of the United States, or by a person authorized to administer oaths whose authority is proved by a certificate of such an officer.