I'm accessing XDA only by two means: On PC/tablet via Firefox, on my Android handhelds via XDA labs. On PC, I don't mind the signatures at all as the size of the screen is sufficiently large. And at XDA labs, the signatures don't appear at all... On XDA labs, you must tab the avatar of the member who posted to review his signature.
In order to end on-topic: I realised that the possibility to donate to become add-free isn't available (or at least not shown) anymore. I remember that you could donate to get another user or yourself add-free.