I was checking out the Wikipedia page for the MK series the other day on my lunch hour and came across this hilarious bit of info. Here it is copy and pasted:
The Sega Mega CD version also contained an additional code (known as the "Dad's Code"), which changed the names of the fighters to that of characters from the classic BBC comedy series Dad's Army.
Source: http://en.wikipedia.org/wiki/Mortal_kombat (Quote is from the Easter Eggs and Secrets section)
I looked around the Gamefaqs page for the Sega CD version of this game and nothing is listed about this. It is probably a hoax. But I'm hoping someone can confirm that this, clearly the most awesome and useful of codes ever devised, does indeed work. While I'm waiting, I'll be ordering my DVDs of Dad's Army from Netflix. (Or whatever the hell they're calling it now.)