United States. Congress. House. Committee on Post Office and Post Roads & ProQuest (Firm). (1921). "International Aero Congress" cancellation stamp at Omaha, Nebr. [publisher not identified].
Chicago Style (17th ed.) CitationUnited States. Congress. House. Committee on Post Office and Post Roads and ProQuest (Firm). "International Aero Congress" Cancellation Stamp at Omaha, Nebr. Washington: [publisher not identified], 1921.
MLA (9th ed.) CitationUnited States. Congress. House. Committee on Post Office and Post Roads and ProQuest (Firm). "International Aero Congress" Cancellation Stamp at Omaha, Nebr. [publisher not identified], 1921.
Warning: These citations may not always be 100% accurate.