For some people, the risk is half the thrill. In other cases it may be the manufacturer making a mark that is distinctive and non-erasable, something like a trademark, so that they can tell if their work has been pirated. Similar to map makers who put in fictitious towns or deliberately mispelling the name of towns to prevent illegal replicators from profiting from their work by copying and not giving credit to the original publisher. It has precedence in the publishing world.