I understand that you want this option or even better a generalisation to all signature campaigns as a whole. So this isn't going to be just for you but the rest of the users to be more easily recognised.

To be honest, you're right that personal avatars will make users easier to remember, spot, or follow but as I see it there's no much that it can be done about it. Signature campaigns are optional anyway, and if you really don't want to change your avatar you can say so (some people might accommodate for that) but in my opinion not wearing the avatar just doesn't get the full attention deserved by the signature. This is why I think on this topic you might be representing a minority...