Right so, i started a couple of campaigns right and never got this option (until i used cheats in one just to see what would happen, so i spammed mercs and took a castle for myself) but when i chose the options, son of an impoverished noble, squire and loss of a loved one... i could pick my own banner...
I'm pretty sure in a previous campaign i picked the same ones but different one than loss of a loved one.
Are there any other little surprises in different mixtures of starting options?
Because using this option, i've managed to become a vassal of the Nords in less than 14 days.
I won the tournemant (it's so easy) i did a couple of missions and the king loved me.