I don't remember how I learned it, but back when my family had a IIci I remember there was a startup key command you could press to display an image of the developers in the ROM. I kind of miss the days when that sort of thing was done.
As a kid I didn't have Internet yet, but somehow had a CoCo3. Many times I pressed Ctrl+Alt+Reset and wondered what was the purpose of this image, I even made a BASIC program to dump it on tape from the ROM. Didn't learn the answer to that mystery for many years.
On the Sega Master System there was an entire game in the ROM -- Snail Maze (the walls and floor reminiscent of the company's logo). Pressing up-left and both buttons while turning on the console with no cartridge in the slot would start the game.
On the Macintosh Classic, there's a whole OS boot disk image in ROM that can be activated by booting with the keys "command option X O" held down (X-O was the code name for the machine). These are the remains of a prototype for making a diskless terminal Macintosh. It comes in handy if you've hosed your boot disk somehow.
