Fuselage ID/formation lights. Usually in two positions on both port and starboard sides. Not sure if these were unique to the 357th FG but after taking a quick look though my Mustang pic database, I seem to only find them on *some* late war D's of the 357th. One in basically the center of the star and the other, forward one right by the data block. Both can be seen in the picture below. I also have some starboard shots of some other a/c ("Butch Baby" being one) where both can be seen as well.