Google has decided to remove the feature of "Onsite Advertiser Sign-up",which allowed advertisers to sign up for AdWords,from your site, as according to them it hasn't been performing as well as they had hoped.However,AdWords advertisers will still be able to target your web sites by using placement targeting.According to the "Inside AdSense Team":"We have high standards for the services we offer, which means we constantly reevaluate existing features to ensure they are effective as the AdSense product continues to expand.We want you to earn more revenue, and sometimes that means "sunsetting" certain features we created. We've elected to gracefully retire this feature and focus our efforts on developing and supporting features that drive better monetization results for you.You may read the full article here.