The Four-cent Prexie
Airmail return receipt
A return receipt could be returned via airmail for the appropriate postage. Before January 1, 1949 this would have been at the first class airmail rate. The situation is not clear for the period between January 1, 1949 and November 15, 1949, when an announcement was made to the effect that the postcard airmail rate would apply.
This receipt was returned airmail from Baltimore to Guam in 1955 for the then-current postcard airmail rate of four cents.