Note: This is the old DOS game from 1989 that is the same as the NES version (but for various reasons is much crappier), not the newer one from 2003.
The Story: I used to own the DOS version of the original TMNT game, which was a port of the NES game. However, the DOS version was almost impossible for me to play both due to the lack of a joystick (keyboard is just too awkward to use) and the fact that my old IBM clone ran it much too slowly. I got frustrated with the game and started mashing on the keyboard. To my surprise, I did something that made me both invincible and able to walk through some walls. In looking up information on this game, it appears that pressing A + S + D + F + G + H activates a walkthrough-walls code and pressing Q + W + E + R + T + Y + U + P activates an invincibility code. My keyboard-mashing somehow activated both codes. (You'll know the code worked if you see "ON" or "OFF" flash at the bottom of the screen.)
When I got to Level 2, the infamous underwater dam level, I discovered you could swim through the walls here with the code activated. As I started swimming through them, I got sucked up off the top of the screen and couldn't get back down. But that's not even the weirdest part. There were two names written in huge block letters written on the screen in the area I went through. One name was written above the other with a symbol in-between them (thought it may have been a plus sign +). Years later, I couldn't quite remember what the names were, but I was pretty sure the one on the bottom was "MIKE". Problem is that I no longer have that IBM clone nor the game disc, and the NES version doesn't have those codes (I somehow doubt the names would be in the NES version anyway, as I think that one was made in Japan whereas the DOS version must've been ported by Americans.) Therefore, I was never able to confirm this memory nor find out what the second name was.
Years later I finally figure out how to use DOSBox and I get a ROM of the game. I get the codes to work, cheat my way to Level 2, and sure enough...
There they are!! (Okay, so it's an "&" between them, not a "+", and the first name is DEAN, but I was close.) To see them, just go straight up through the wall from the first screen of the underwater level.
And this screen is actually one just below them, though I don't remember seeing that years ago. Could be that I saw it and forgot about it, or I somehow worked around it. These screenshots are from the 4-color CGA version that I had. Here are some screenshots of the same scenes from the more-colorful EGA version:
So who are DEAN and MIKE?
They are two of the graphics artists that worked on the DOS port.
Incidentally, I never made it past level 2 on the DOS version because the control was impossible to deal with and I could never get all the bombs in time. This level is known for being somewhat difficult on the NES version, but it's a piece of cake compared to this one. Actually, though, I think a huge part of it was how slowly my IBM clone ran the thing. It didn't seem as difficult when I played it on a modern PC with DOSBox, but on my XT it was so slow that the controls would severely lag.
However, it's probably just as well that I gave up on it. According to Scary-Crayon, there's an impossible jump later on in Level 3 that denies further progress, unless you use the walk-through walls code to bypass that area. If you're interested at all in playing this game, I'd recommend getting the NES version and skipping this one.