When you get into the very first section go to GIL'S sign. Its near the first helicopter hive. All you have to do is shoot the L once, followed by the O. Than the L again.
Once done LOL will appear on the screen in multi-color text. And for a duration after all aliens will pop out a bunch of alien shaped teddy bear like things when they die. When it stops happening you can just go to the other side of the sign and shoot those LOL and it will activate again,IT:
EDIT: MUST BE DONE WITH A SNIPER RIFLE.
i noticed the lol but never thought to shoot it gonna go try this
just saw a guy do it in my game it works its the back of the sign faceing the hive and u may need the sniper not sure if its needed
meh cant get it to work myself but ive seen a guy do it XD