No One Lives Forever Easter Eggs

Now, all you need to do is start a mission. Anyone, your choice. Then, press "T", the send message button, and type: mpmiked.
It will ask if you want a lot of money. SAY NO!
Then, a voice will come on and play a cool song.

Play the game to the beginning of part 3 of the mission "The Dive". During a cut scene to set up the next action sequence, a submarine comes into view. The sub's designation is "5675 - 309". Somebody's an 80's rock fan.