I know the system doesn't allow you to register with the very same username somebody else uses, and that you can't implement some automatic way to stop "similar" names. What I meant is that in the case where there can be some confusion (which means when the similar name is used by a usual poster), the name should be manually edited, just like the Judge does with sigs.
I was talking specifically about J_Hendrix, he even mentions JHendrix in his sig, that by the way looks like was edited by the Judge.
About avatars, I see no problem in using the same one as another user (as long as your name is not similar to his), specially if is one of the generic public avatars. Make your own one if you want it to be exclusive.