I sat through all the credits (to the very very end--I didn't appreciate that the theatre brought up the houselights as soon as the credits started to roll) and I saw the sneak peak. But I didn't see any ad--unless people mean the bit in the credits that says something like Green Lantern appears in DC Comics, which is standard for all DC movies. Was there supposed to be an ad?

It woulda been nice if they had played "Sunshine Superman" over the credits.