To those who were not familiar with this feature, this is a special link on the bottom of Google adsense advertisements posted to websites. On the Inside Adsense blog: Farewell Onsite Advertiser Sign-up , it was announced that they already removed this feature. Although this is a great idea to gather and invite advertisers to sign-up, placing it on the ads itself is obviously not effecitive. Why? simple. It is not themed to the majority of the ads shown. Adsense promotes the relevancy of the ads to the theme or content of the site so visitors will be enticed to click on the ads. That’s the primary purpose of online advertising.
To the vast majority of websites, I think not every website is relevant to advestising on a PPC (pay per click) and if a visitor is willing to advertise on the site visited, his or her first thought is direct advertising. But when the visitor clicks on it he is redirected to Adwords to sign-up and have to learn the complexities of contextual advertising. So the visitor backs out. Unlike the simple transaction of placing a banner or a text link on the site itself. ( To see the clearer picture, read the discussion on Webmaster World ) But on the contrary, still contextual advertising like Adwords is the best way in online advertising.