The bent parking meter in season one.
The mention of the volcano god in the Philippines in ep202. (reference to "Monkeys Violating the Heavenly Temple")
there's lotsa more, right?
My Friend: You know, if only Bruce Wayne was bit by a radioactive psychiatrist rather than a bat, Gotham wouldn't even need Arkham Asylum.
Me: Haha, yeah. That's true.
Me: Wait, Bruce Wayne was never bit by a radioactive anything.