In the US: Wings

Wings are perhaps the most universal symbol of flight, and early US Air Mail stamps have incorporated wings into their design.
The 1932 US Air Mail Issue, C-17

A new air mail rate of 8 cents per ounce went into effect July 6, 1932. This stamp was issued for this rate on September 26, 1932 in Washington, D.C.
The 1934 US Air Mail Issue, C-19

This stamp was issued in 1934, repeats the design of the 1932 issue.
The 1932 US Trans-Atlantic Issue, C-24

This stamp was issued on May 16, 1939 to commemorate the beginning of Trans-Atlantic air mail. The winged-globe Insignia from earlier designs is shown above 2 ships on the Atlantic.