So it may not be the greatest Easter Egg, but it is probably the coolest Easter Egg and nod to Batman's cinema history in Batman v Superman: Dawn Of Justice.
Let me explain:
In Christopher Nolan's The Dark Knight Rises, Bruce Wayne plays certain notes on a piano to gain access to the secret entrance that leads to the Batcave.
Here are these notes from the 0:06 minute onwards:
Now, this is where it gets interesting.
In the Batman v Superman: Dawn Of Justice score that is composed by Hans Zimmer and Junkie XL, there is a track called "Beautiful Lie." This is the first track of the film and depicts the rise of Batman.
Towards the beginning of the track and the end, the piano and trumpet respectively are the same notes/tune used in the entrance to the Batcave in The Dark Knight Rises.
Check it out below:
How cool is that?
Not only is this an awesome nod/tribute to a fantastic superhero trilogy but goes to show that Hans Zimmer (also the composer of The Dark Knight Rises) is one sneaky devil.