I knew this would get confusing.
So basically people are finding symbols of the games in the sale in each other. As well as more potatoes. Example: On the back of a character's jacket in Killing Floor, there is a symbol that resembles the The Ball logo. On the walls of the catacombs in The Ball, there's a symbol that resembles the logo of Defense Grid. You get the idea. If you want to try yourself, the easiest thing you can do is play the Super Meat Boy track "The Battle of Lil' Slugger" in Audiosurf. A giant potato will be present, with glyphs across the skin.
Things continue to happen.