Somewhat related, while using a program to edit deep code and other things in (edit)The Sims 2 program SimPE I came across a photo of a Mr. Potato Head, when I confirmed this on a Sims 2 Chat room in front of people that mod the game, they just laughed at me, and the feeling was like, maybe they were laughing at me for having some kind of malware on my system.
on topic though, sometimes developers leave things in video games sometimes only a programmer or someone who studies the code can find. And other times it is somehow seen through cheating, like on Duke Nukem 3D Episode 1 level 5 where if you jet pack across an otherwise impossible section of the level. there is some writing on the wall say in in quotes "How Did You Get Here?"