I think you've portrayed the concept quite nicely. You know how there's like smoking signs with a red circle around a cigarette and a red slash going through it? Well this piece is kind of like that but instead of a slash it's a peace sign. You could possibly make the border lines redder to establish the No Warmongering sign :)

Hmm i hadn't thought of that one but i like it. I was thinking something more on the lines of peace not war I just can't seem to come up with a way to portray that... this was my first try at it.