I have video evidence it was used during the Korean War.
I was watching a documentary about the F-86 Sabre, called "Great Planes," which was produced by the Australian Broadcasting Corp., (this may be why the gesture got past the censors). They were showing footage of a squadron of F-86s preparing for a mission during the war and I noticed, as each jet taxied past various people on the ground, the people were all smiling and enthusiastically waving their hands at the jets. Then I almost spit my drink out when a guy standing by a jeep, which was labeled "flight surgeon," clearly waved his middle finger at the passing jet. At this point I noticed the aircraft numbers on the tails of each jet and figured out the joke.
You can see the footage at the 24:00 minute mark here
I guess every generation thinks theirs’ is the first to come up with certain well known signs, symbols and lifestyles.
Now I know better.