I have added a scar onto my character's face marking the strike you lay on him after he showed you mercy as you surrendered, and then attacked him!
That event has changed my character significantly enough for me to add physical mark. He now feels less able to show mercy to members of the Selgovae who surrender, as he feels they will lie and not keep their word.
You can go brag to your Selgovae buddies that you've left a mark.