Girls with guns are not inherently violent. Many people enjoy shooting as a sport and never kill or harm any living creature (well OK maybe some bacteria, but they don't count :p ). It is really the intent of the caption, the story involved, etc. that make something violent or not. Obviously we don't want pictures of people being shot or the after-effects of a gun wound, but showing guns in the picture does not run counter to the rules. Heck there is a "ray-gun" category of transformations that many people have in their preferences. So I think we are good to show other guns as well.
If this idea becomes a contest, we would need to be careful, but I trust people here to follow the spirit of this place and not go crazy and start killing characters left and right.
Oh and as Alexia says, thank you Sara for bringing this up. It is a very legitimate concern. [approve]