Just a suggestion, could the knights be forced to PM people before they make changes to someones sig or avatar. Even if they still remove it this would allow the user to know what they did wrong and who did it so they can ask them ways to fix it, etc.
Just an idea, why? I have the above problem, I thought my sig was acceptible (It has been left for the last 3 weeks) and then out of the blue without warning it disappears. Anyway, I've already put out an appeal for someone to tell me whats wrong with it, so don't worry bout' that.