Warner Bros' announcement that the sequel to Man of Steel will be a Batman/Superman team-up is big news.  But it is also a totally natural development, one that has been rumored and desired for years.  Charles Roven, a producer on Man of Steel and Christopher Nolan's Batman trilogy, famously denied the possibility in 2011:

"That may be in somebody’s mind but right now the Batman lives in his world and the Superman lives in his world.  Those stories are those stories and we haven’t thought beyond each individual picture."

I would change the wording a bit to say "That may be in everybody at Warner Bros' mind," because we have seen Easter eggs that hint at a Batman/Superman crossover in many recent WB properties: Man of Steel, The Dark Knight Rises, Superman Returns---even I Am Legend and Fringe.  Follow the trail after the jump.

[This post contains spoilers for Man of Steel and The Dark Knight Rises]

Let's start with the most convincing and---not coincidentally---most recent.

Man of Steel

Zack Snyder revealed before the release of Man of Steel:

“The Wayne Enterprises logo is on a satellite that Zod destroys.”

We will have to wait for the DVD release for a good, legal screencap, but the director's word is good enough for now.  This suggests the Batman/Superman crossover was somewhere around Likely by post-production on Man of Steel.

Additionally, Dosis Dei [via Bleeding Cool] noticed interesting design hidden in Jor-El's costume in Man of Steel.

Whoa!  I feel reasonably sure that is an intentional Batman logo.  This next logo...not so much.

The Dark Knight Rises

ComicBook.com sees the Superman logo in the Dark Knight Rises poster.

Don't see it?  Me neither.  Let's zoom in:

A bit of a stretch, but maybe if you squint through your hindsight glasses.

Superman Returns

To get back on solid ground, there is a news segment in Superman Returns that highlights Superman's visits to various cities including Gotham, Batman's stomping grounds.  (Sorry, couldn't find a clip, but it's well-documented.)  Pretty straightforward---now let's get back to the more obscure.

I Am Legend and Fringe

In I Am Legend, there is a billboard in a deserted Times Square with that combines the Batman and Superman logos:

In an alternate universe in Fringe, Warner Bros. is already on Superman vs. Batman 2 [via i09]:

Unfortunately, The Hex of the Hydra remains in the alternate universe where revisiting Indiana Jones 20 years later isn't sad.

Back to The Dark Knight Rises

We can file the final item under Unlikely But Fascinating.  Some took issue with a couple apparent shortcuts at the end of The Dark Knight Rises.  1) How did Batman get from the prison located on the other side of the world back to Gotham unnoticed, without access to his vast resources?  2) How did Batman escape alive when we see him on The Bat with seconds left until a nuclear bomb detonates?  Nerve Protein posits a crazy but well-reasoned conspiracy theory:

"Perhaps [Batman excapes] with the help of a stranger he met in his travels back to Gotham? Perhaps the very same person who helped him return to his city to save it from certain destruction? Someone with whom speed is not an issue? Someone who also shares an alter ego?

I’m talking of course about Superman."

This would be terrible storytelling, to leave the story ostensibly unfinished before revealing several years later, "A Superman did it."  But picture a flashback down the line where we see Superman fly Batman to safety, chased by a nuclear explosion.  What a payoff!

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Hope this was a fun diversion.  Do you see any I missed?  Can you find better evidence for the reference to a "man seen flying" in The Dark Knight Rises than I did?