The biggest tease of Gotham [1]'s first season surrounded the identity of Batman's most infamous nemesis: the Joker. Actor Cameron Monaghan, who played Jerome last season, a guy who was almost definitely maybe the Joker, posted a picture of himself reprising his character. He hashtagged it simply, "#Gotham." Between this and Bruno Heller's comments [2] about answering questions about the Joker in season two, we can deduce that yes, he's back, and yes, Jerome is the Joker. Then again, Gotham is full of red herrings!
#Gotham [3]