How, when we getting custom skins, may be it is a good idea to make also a visible kill markings. Though they will be hardly visible in game during fight, they shall look amazing at the planes for screenshots and films, and will be a very nice immersion moment for AH2: TOD.
Just put correct signs ( stars, crosses, vertical columns ) at correct places ( side of plane, tail of plane ). When there are too many of kills, add 50, 100, 150, 200, 250 etc. and markings.
Shall be one dinamicly pre-flight generated texture, I am sure it is not hard to code, and one textured poly will not put much more stress to the video card.