The patches on their leather jackets
The main characters all wear A2 leather jackets during the first half of the movie. The jackets have various patches on them. Two of them wear "Ad Inexplorata" patches which are the insignia of the Flight Test Center at Edwards Air Force Base. There are also 17th and 380th Bomb Wing patches which were both Strategic Air Command units during the cold war. I would assume that these were privious units in which the characters had served in prior to joining Team D. The Army Air Force officially dropped the A2 at the end of WWII in favor of the B-15, L-2A, and eventually the MA-1 flight jacket. Unofficially, many Air Force pilots have continued to wear the A2 for various reasons.
"Who knows, Mr. Gilbert, what a limit really is." Lincoln Bond, "Toward The Unknown", 1956