I don't think that many people click on random signatures anyways. Perhaps only on those from high-quality members that are instantly recognizable.
True, people barely click on signatures. And if a campaign evaluate the result with the clicks from the signature tracking link, they will simply stop running campaign here because the conversion rate from the tracking link will be too low to evaluate even. I can't remember if I have ever clicked on any signature to join a casino or check out a mixer.