To quote Joseph Visscher
'Good idea guys, but I donít know if it will be implemented, maybe it will, I doubt it. We will most likely make something unique for each player to be identified. But so far, we just have unit colors and the and markings are unique for each faction, each faction has their own flag design.'
Hope this has been of help, Also yes it has been discussed several times, just search flag/banner/logo/colours and you should get some results for it. I got it from the simple search of 'flag'
Xbox live gamertag: WelshAbyss
Feel free to add me and game to our hearts content :)