So I pick up and have been playing Arkham City for the last two days now. Awesome game and I'm loving it 100%. Anyways I was messing with the Cryptographic Sequencer (the radio signal thingy) and I stumbled upon a signal (at 689, 500 if you are interested). The code is this: 9 23 9 12 12 18 5 20 21 18 14 2 1 20 13 1 14. I noticed that all the numbers are under 27 so I figured number to letter conversions were in order. I converted them and got the following message: I Will Return Batman...So yeah. I think I'm the first to discover this (Yay for me!). No idea who the speaker is but It's very ominous.