When browsing the OpenStreetMap Wiki, I ran across a page called Maps That Lye, which contains information about anti-copying provisions in maps. In particular, there are a number of locations on many maps that are intentionally wrong or misleading in an attempt to make it obvious (to the copyright holder) when maps or map data are copied. (Of course, if all map data were accurate, it would be almost impossible to tell that you had copied the map).