Italy: Issued June, 1917 by the Aero Club of Palermo (and) the same design was also issued in 4 bicolor stamps by the Palermo Philatelic Club ... listed in Landmans'
Catalogo Delle Cartoline e Vignette Ufficiali e Semiufficiali di Posta Aerea Italiana... They are not listed in Sanabria as semi-officials, so I suspect they were of a commemorative nature. The surcharged varieties are listed in Mosbaugh's "Red Cross Seals of the World" catalogue.
" [Ray Petersen] via [rs]