If you have Google Shopping campaigns and would like to have the Special Offer tag show for a Google Merchant Center Promotion then you need to be fill out this form
. These are available for Google Shopping in the US, Australia, France, Germany, India, and UK. All you will need is your Merchant Center account ID, name, and your listed homepage URL. Once your application is approved you can add a promotion via a feed or by using the +Promotion button and filling in the fields. Google Shopping promotions help your product listing ads stand out and therefore convert more.