A pioneering Italian aviator, Italo Balbo (1896–1940) made a number of mass formation flights in the late 1920s and early 1930s. His South Atlantic crossing from Rome to Rio de Janeiro in 1930–31 with a formation of Savoia Marchetti flying boats is commemorated by this stamp, which shows the seaplanes with the Southern Cross above. My criterion for a truly realistic Southern Cross is that it should show all five main stars, but this goes one better by showing a sixth, Zeta Crucis. 

This is an expensive stamp, and used versions cost considerably more than mint ones. There is a rare design variant, now almost unobtainable, that shows a seventh star – one stamp per sheet of 50 had this additional star. 

A subsequent and even more celebrated Balbo flight, across the North Atlantic, is commemorated by a 1933 stamp from Cyrenaica.