As used in this chapter—

(1) “penalty mail” means official mail, other than franked mail, which is authorized by law to be transmitted in the mail without prepayment of postage;

(2) “penalty cover” means envelopes, wrappers, labels, or cards used to transmit penalty mail;

(3) “frank” means the autographic or facsimile signature of persons authorized by sections 3210-3216 and 3218 of this title to transmit matter through the mail without prepayment of postage or other indicia contemplated by sections 733 and 907 of title 44;

(4) “franked mail” means mail which is transmitted in the mail under a frank;

(5) “Members of Congress” includes Senators, Representatives, Delegates, and Resident Commissioners; and

(6) “missing child” has the meaning provided by section 403(1) of the Juvenile Justice and Delinquency Prevention Act of 1974.