According to CTV News, franking refers to a mark or signature on an envelope signifying it is to be mailed free of charge. The United States Committee on House Administration states that franking dates back to the 17th century.
In 1775, the American Continental Congress stated that franking was needed for Congress to inform its citizens easily without the hassle of purchasing postage. During the 19th and 20th centuries, franking was controversial and at times was frowned upon by the United States Postal Service. As of June 2014, Congress members are allowed to use any portion of their budget to mail necessary items.