How can I set up the Onsite Advertiser Sign-up feature?

How can I set up the Onsite Advertiser Sign-up feature?

We're sorry to inform you that the Onsite Advertiser Sign-up feature is no longer available. The 'Advertise on this site' link no longer appears on any of our ad units. If you included direct links to this feature on your site, please consider replacing those links with text links for AdWords referrals. AdWords referrals can help you earn as much as $45 for each new advertiser that signs up via your site. Any existing direct links you've pointed to the Onsite Advertiser Sign-up landing page now redirect to the main AdWords sign-up page where prospective advertisers can buy media and compete in the auction, driving up demand for publishers' content.
As the AdSense product evolves, we occasionally re-evaluate aspects of the product to make sure they're performing well for our publishers and meeting our goals. We found that OASU links were under-performing, and so we've made the decision to focus our efforts on features that will drive the best results for publishers.