San Francisco, Cal/M.P.O. (Model Post Office). Oval handstamp (Bomar SF15-05A) on reverse of 2¢ Postal entire postmarked with San Francisco Panama-Pacific/Apr. 10, 1915 machine cancel slogan cancel to Denver, Very Fine and rare, one of three recorded examples of this rare Expo. marking, one is known as a favor cancel, one is known on a label & this example. Estimate  $500 - 750. $0 (Image)