USA
Returned for Additional Postage

U.S. 11c aerogramme (Wiegand no. 11, pale blue paper) issued in 1966.
Used from CHICAGO (cds Oct 18 1967) to Tel Aviv, Israel. 

Since May 1, 1967, the rate for aerogrammes was 13c. Hence, the aerogramme was h/s “Returned for 2 cents additional postage / Chicago, Ill. P.O. Forgn. Sec. I” and returned to the sender. 

A 5c stamp was affixed, overpaying the required postage by 3c.  Most likely, the sender did not have a 2c stamp available and therefore used what she had at her fingertips.

References
Wiegand refers to Wiegand, Katalog der Aerogramme von Canada, USA, UNO-New York, 1994