Thank you.
Responses covering more regions/cultures of Medieval Europe are welcome; meanwhile you may be interested in these
In Denmark-Norway there was a tradition in the 1500s-1600s to name the illegitimate sons and daughters of the king Gyldenløve (literal translation to english would be "Golden Lion".
Christian IV, Frederik III and Christian V of Denmark all had several children by various mistresses who all carried the surname Gyldenløve.
So at least for Danish royalty there at one time was a "system" of naming bastards if you will.
There's a sports reporter called Dan LeBatard and I've always wondered if his ancestor was a Bastard. Does anyone know anything about this name?