It could be an Indy decal. As I recall the 1978 Indy Pace Car Replica by Chevrolet, it had a winged decal on the rear fender, each wing about 4 inches long and something vertical in the center, maybe a tire front 3/4 view.
You can see it on this website
http://www.indypacecars.com/1978.htm
I think that logo has been used on Indy cars for generations. Now what it would be doing on a Cobra big block prototype is anybody's guess except that it is well known some Shelby shop employees were ex-USACers and thought any car that wasn't a full-on race car wasn't worth much, so maybe they stuck it on to say "At last we got a car that's worthy of being a race car."
I could print it out and send it to Phil Remington at AAR and see if he remembers since he's in some of the pictures and was there when it was tested or is there someone else who remembers the car when it was in prototype form?