Action DooM! Easter Egg - Linguica's Album

In the first interactive level, where you are fighting your way through the city, stop when you reach the second point where the roads part. If you look up and to your left, you will notice a Billboard advertising Action-Beer.

Use the noclip cheat-code to scale the building the board is based on, and shoot the board. Step back, and you will notice that the billboard has become an advert for Linguica's Music Album.

Linguica is rather famous in the Doom community for being an active and creative person. He composed much, if not most, of the music for Action-Doom.