Franked mail does not use official postage; it can be identified by the signature of the authorized person who sent it. A franked envelope is official government mail that can only be used by members of Congress, the vice president and other authorized officials.
Franked mail is regulated by the Commission on Congressional Mailing Standards. The body also hears formal complaints when someone believes that a member of Congress has violated the rules.
Franked mail sent to 500 or more constituents must include a statement that the mailing was sent at taxpayer expense. Offensive language or derogatory statements about another member of Congress are prohibited.