APA (7th ed.) Citation

United States. Postmaster General. (1927). New 20-cent air mail stamp. U.S. GPO.

Chicago Style (17th ed.) Citation

United States. Postmaster General. New 20-cent Air Mail Stamp. Washington: U.S. GPO, 1927.

MLA (9th ed.) Citation

United States. Postmaster General. New 20-cent Air Mail Stamp. U.S. GPO, 1927.

Warning: These citations may not always be 100% accurate.