United States 1926 Alan Cobham Peri-Columbia Demonstration Flight Signed Cover. 1926, Cobham Pre-Columbia Demonstration Flight, 2c postal stationery cover, postmarked Washington D. (Dec 4), with blue “Cobham First United States Overlight Flight” handstamp, signed Alan J. Cobham in ink, an uncommon signed cover, very fine. Member of the Canadian Stamp Dealers Association. Are the responsibility of the purchaser. Our Guarantee to You… We’re proud to offer collectors an attractive selection of fine and rare stamps, postal history, and ephemera. We seek out quality material for our clients. _gsrx_vers_1436 GS 9.0.5 (1436).