Crimson skies: High Road to Revenge Easter Egg - Police Code in Chicago

Play the game until you get the the Chicago level where Kahn has kidnapped Betty and you're supposed to find her.

Exit the Pandora and fly to the left. Go to the other edge of the city, where you will find a big, modern-looking police zepplin with pointed ends.

Fire a couple of shots at the zepplin with your primary weapon, pull away, and listen. You should hear the words "Looks like we got a 420 in progress -- the perp is one Nathan Zachary -- let's smoke him, Boys!"

(Funny because "420" is a well-known code word for marijuana and the cops are going to...well, "smoke him".)