B. Free Franklin Post Office, 316 Market St. within Independence National Historical Park, commemorates Franklin's 1775 appointment as first postmaster general. Said to be the only post office operated by the U.S. Postal Service that does not fly the American flag, it is named after Franklin's unique signature. It is assumed that his use of Free as part of his signature referred to America's struggle for freedom. Philatelists prize the hand-canceled letters from this post office.