Ok so everyone already knows about the dials in the light house and the code but it may be more than just entering the code. A friend and I just found some horns on the ground outside the light house that when you press x when you are near them they make different tones that correspond to one of the dials. So each of the four horns goes with one dial. So perhaps there is more than one easter egg if you get the dials right and then active all the horns at the same time. I can't confirm this just found it a little bit ago in a two player game. Two of the horns are located near the ak74u and the other two are located in the water area past speed cola.

whtout23