An entry at Folklore.org by Andy Hertzfeld, a key member of the original Macintosh team, provides an interesting insight into the lengths that the company went to to protect their intellectual property. In this case, the Macintosh ROM:
In 1980, a company called Franklin Computer produced a clone of the Apple II called the Franklin Ace, designed to run the same software. They copied almost every detail of the Apple II, including all of its ROM based software and all the documentation, and sold it at a lower price than Apple. We even found a place in the manual where they forgot to change "Apple" to "Ace". Apple was infuriated, and sued Franklin. They eventually won, and forced Franklin to withdraw the Ace from the market.After the incident with Franklin, Steve Jobs decided to protect the ROM by embedding a small token into it that could be displayed in court during a trial. The idea was that he would be able to enter a few keystrokes on the offending machine and display the token, proving unequivocally that the ROM was stolen from Apple.
Susan Kare designed the "Stolen (c) Apple" icon (pictured above) and Steve Capps compressed the icon and wrote a routine to decompress and display the icon on screen. The team hid the little nugget of code in the "middle of some data tables, so it would be hard to spot when disassembling the ROM."
To display the icon you have to enter the debugger on an original Macintosh and enter a secret 6-digit hex address, which according to the comments on Digg.com involves pressing the programmer switch and entering G 40E118.
The secret Apple ROM icon reminds me of the technique that cartographers use to protect their maps by adding fake streets, so that if anyone copies their work, they can easily prove it in court. If you've got an original Mac 128k around give it a shot and post your screen shots in the Talkback comments below.
What's your favorite Apple easter egg?