He is saying Hi, and in that billboard is something you read in the first Oddworld, Abe's Oddysee, and it says "If you escape, all 28 workers on this level die!" This is not complete BTW.
Edit: I did mention I drew this right? Yeah...I don't think I did...
On the left is a close up FYI >.>
Moddb.com
remember blowing them up with your mind?
I sure do. =D I also like just running around as them...I feel safer =O