1918, $2 orange red & black. In combination with 1917, $1 violet brown + 1918, 16¢-24¢ airmails + 1923, 16¢ airmail on Round the World Zeppelin flight cover, all tied by "Varick St. Sta., N.Y., Aug 6, 1929" machine postmark and oval handstamp, purple circular flight cachet and green receiving flight backstamp, Very Fine; with 2007 P.F. certificate. Scott No. 523+518+C2-C3+C5  Estimate $1,000 - 1,500. $0 (Image)