"It sounds like a conspiracy theory, but it isn't. The pages coming out of your color printer may contain hidden information that could be used to track you down if you ever cross the U.S. government.
"Last year, an article in PC World magazine pointed out that printouts from many color laser printers contained yellow dots scattered across the page, viewable only with a special kind of flashlight. The article quoted a senior researcher at Xerox Corp. as saying the dots contain information useful to law-enforcement authorities, a secret digital "license tag" for tracking down criminals."
More here at the Washington Post.