Cita APA (7a ed.)
United States Postal Service. The Postal Service Guide to U.S. Stamps.
Cita Chicago Style (17a ed.)
United States Postal Service. The Postal Service Guide to U.S. Stamps.
Cita MLA (9a ed.)
United States Postal Service. The Postal Service Guide to U.S. Stamps.
警告：这些引文格式不一定是100％准确.