This envelope signed by Thaddeus Stevens, then the powerful Chairman of the Ways and Means Committee, is an example of the use of the “franking privilege,” which allowed Members of Congress free postage for official business. The Member’s signature and stamp reading “free” was the simple format for postage leaving the House beginning in the late 18th century.
History, Art & Archives, U.S. House of Representatives, “Free Frank Envelope,” https://history.house.gov/Collection/Listing/2004/2004-078-002b/ (July 02, 2022)
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