United States. Post Office Department, United States Postal Service. Directives Control Division, United States Postal Service. Directives and Forms Division, & United States Postal Service. (1918). The postal bulletin. Post Master General.
Chicago Style (17th ed.) CitationUnited States. Post Office Department, United States Postal Service. Directives Control Division, United States Postal Service. Directives and Forms Division, and United States Postal Service. The Postal Bulletin. Washington, D.C.: Post Master General, 1918.
MLA (9th ed.) CitationUnited States. Post Office Department, et al. The Postal Bulletin. Post Master General, 1918.
Warning: These citations may not always be 100% accurate.