Doom 3 Easter Egg - Hidden Message on Broken Keypads

In the first few levels you will encounter rooms with the pentagram symbol on the floor surrounded by candles where a demon will spawn from. The rooms have keypads to get into them but the doors are open already and the keypad is broken. The keypad will blink red. If you look closely you will see text saying something like enter security code. Since the pad is broken it blinks a lot. When it blinks the text quickly changes and says something like "Hell will kill you" you have to be very quick to see it but after looking at it for a minute you will see it.