Mandarin has a Captain America shield with an Avengers "A" in the center on the back of his neck... my guess is that Marvel will be giving the same treatment to its villains as it did with the Avengers themselves by slowly introducing the villains in the after credits scenes. Could we expect to see the Masters of Evil in Avengers 2??
It was mentioned in an interview a few months back that they are going to introduce Ant-Man and Radioactive Man in the end titles thing of Iron man 3. So it does sound like you theory is correct.