This mark was changed with the alteration of faction points. Not sure how much you need now, I hit 22595, was given Legendary status with the Knights of Chanctonbury and was not granted mark. I no longer get any faction points when I kill orcs so may be another way or it was just never fixed when the change was made.
As of 2/23/2012, it still is not granted by reaching maximum faction. It might be given after you've killed x amount of orcs, which is speculated at 100 kills.