I noticed the two green birds before. Never gave them much thought though. After reading this thread I found hat-less Cole sitting on the roof below the second green bird to the right of Ser Barris.
As for the "easter egg" definition, I assumed it referred to something hidden in gaming; either a secret cheat, inside joke, or just something not easy to find. A shame people use this thread to argue the semantics of a term rather than comment on the discovery.
Yeah I think it's supposed to be Envy, but it's still damn creepy! Lol
It could have been an easter egg if say you saw someone from Mass Effect walking in the crowd, but because of the option to say you saw Cole, I think it was more of a "if you spot him good for you, if not... surprise!" I have to admit, after I realized he was there, I kept watching in the background right up to the moment with Envy to see if Cole showed up anywhere else. LOL