Cisco allegedly did something similar when it suspected Huwei was usign it's source code. They added some minor typos to error messages and then check the Huawei routers and sure enough they had the same mis-spellings.
Since no one programs against the textual strings of the error messages, they jumped to the conclusion it was source code theft and not a clean room implementation that Huawei was using
> "A spokesman from the service told Australian newspapers that while some map makers intentionally include phantom streets to prevent copyright infringements, that was was not usually the case with nautical charts because it would reduce confidence in them."
This way, if someone copies your map, you can prove they copied you. If your map was totally accurate, then they (the copier) could claim that they went out into the world and surveyed it. If they include your trap street that only exists on your map, and not reality, then it must be a copy.
Melway is a company that makes excellent street directories for all the major cities in Australia. It came out a while ago that on every single page, there are intentional errors that would help catch someone copying their maps. There was a phone box marked on my street that didn't exist, and a friend's house was next to a street that didn't exist.
It gained some attention a while back because it could turn into a safety issue - i.e. I rely on the map to tell me where I can find a phone box to call emergency services. They downplayed it.