Warning, the following is a noob question: Do existing sig links stay if you change your sig? Let's say I posted 100 times with sig link A then switched to sig link B for another 100 posts, would I have 100 of A and 100 of B or just 200 of B?
That's what I thought, so for part 2 of the question, why do people sell their signatures? Or why would people buy signatures if they're only temporary links? Is it just for traffic generation rather than link building? I think that answer is obvious but I want to be sure I'm not missing anything.
This is correct, all your previous posts will have your updated sig Sig links are just that, temporary, but most persons who buy sig links renew them for another term, so they are not necessarily temporary if the buyer keeps renewing. Personally I've found that is what sig links are best for, the traffic you get from people clicking the links, and not for the benefit of SEO (though it does help).