Grand Theft Auto: San Andreas Easter Egg - Rockstar North Don't Like Your Kind 'Round Here

During the very last mission of the game, you'll find yourself assaulting Big Smoke's "Crack Den" in East Los Santos just before crossing into Los Flores. After battling your way clear up to his to floor doorstep a battle with Big Smoke will follow. Before or after leaving this big room look at the mat placed here. It says "Not Welcome R* Rockstar North". Just a subtle little tag.