Originally Posted by **********

It's the same reason why banners don't work in most people's signatures either.

If you want people to click on your ad, you have to first add relevant content to the thread that is also relevant to the service or product that you offer. For example, if someone posts a Video Chat software question, I might offer some advice, and then ask that person to click my link or banner. Just like Google, Relevant text and ads are much more click-worthy than irrelevant text / ads. Anyone who paid for sig placement wasted their money.