Famous Apple engineer Andy Hertzfield, writing for Folklore.org, details a story from the early days of the Macintosh, in which Steve Jobs devised a way to out software copiers:
Steve decided that if a company copied the Mac ROM into their computer, he would like to be able to do a demo during the trial, where he could type a few keystokes into an unmodified infringing machine, and have a large “Stolen From Apple” icon appear on its screen. The routines and data to accomplish that would have to be incorporated into our ROM in a stealthy fashion, so the cloners wouldn’t know how to find or remove it.