NEWS
Arkham City Easter Egg is confoundingly complex.
Rocksteady are no stranger to Easter Eggs. Batman: Arkham Asylum contained such forethought that a secret room existed showing plans of Arkham City as overseen by (then) Warden Sharp. So it's little wonder that a game as long and deep as Batman: Arkham City would contain as many easter eggs as it does.
The Easter Egg in question? A series of three number codes, located by using Batmans cryptographic sequencer. Each location on the sequencer gives a masked voice uttering a bunch of numbers followed by a small jingle. The numbers are between 1 and 26, so popular belief is that each number represents a letter.

Only one of the three codes can be unlocked using a simple A=1 B=2 sequence, which translates to an ominous message of 'I will return, Batman.' The other two however, are proving to be more complex. How long will it be before someone cracks the code? Impossible to say, as are what the contents of the encrypted message might be, or what they could possibly reveal.
Just as likely, however, is that the other two messages are actually false gibberish, or red herrings. Yours truly noticed that the three broadcasts form a triangle with Gothan FM at the centre of it, but even that could be nothing of importance.
Arkham City is full of hidden secrets and Easter Eggs, and this is unlikely to be the last of them. The game even has a secret achievement where Batman pays his respects to his dead parents resting place. The attention to detail Rocksteady have thrown into this game is truly staggering.