I agree with fkusumot that its best to find an avatar you like and then don't change it. Signature pics can change if you want to spice things up, but avatar pics get linked to people's names. Subconsciously when you read someone's post you see their avatar pic and often don't read the name, the picture ends up sort of becoming the personification of that person. If the avatar is of a person or character, you can almost picture that person/character writing the post you are reading.