Character mistake: Throughout the series, JD and Turk are shown to be major sitcom geeks. At one point in the episode, JD says to Turk he Marcia Brady'd his ass, and explains what it means. Turk responds along the lines of "Yea, I know. 'Marcia Gets Creamed' Season 5 episode 3. Don't ever question me about The Bunch!" 'Marcia Gets Creamed' is season 5 episode 10. Episode 3 is 'The Elopement'. Not a mistake a couple of geeks would make.
Character mistake: JD is having problems with someone dressed in a gorilla suit, who is slightly shorter than he is. JD sees the janitor, who is considerably taller than he is, eating a banana and accuses him of being the gorilla. If the janitor were as tall as JD, maybe, but you would not confuse someone shorter than you with someone taller, regardless of costume.
Answer: No, it was a fake, they used a stamp.
It is real.