San Diego (Exposition Sta.) Cal./Jul. 26, 1915/Registered. Beautifully struck violet double circle postmark (similar to Bomar SD16-02) on Post Office Dept. Penalty Envelope with rare unlisted violet straight line "Exposition Station, San Diego, Cal." handstamp, cover endorsed in address panel "Compliments of Exposition Station", Extremely Fine, a rare cover which is used in 1915 and is the only known example of this combination of markings. Estimate  $500 - 750. $0 (Image)