Upstairs in the Ghostbusters' HQ there is a kid's drawing on a pink piece of paper hanging by a lot of electrical equipment. It says "To Uncle Egon, from Ed." This is a reference to the fan made Ghostbusters movies "Freddy Vs. Ghostbusters" and "The Return of The Ghostbusters", where Egon's nephew Ed Spengler creates the Denver Ghostbusters.