Giant photocopying firm Xerox has admitted designing its color photocopiers so that they put a hidden code on your copy that will help the US government identify you According to Peter Crean, a senior research fellow at Xerox, all his company's laser printers, copiers and multifunction workstations, put the serial number of each machine in yellow dots on the page.
He told the Medill News Service that the dots only show up if you look at the document with a magnifying glass while shining an LED beam on its surface. This will mean that if any document shows up in a criminal inquiry the spooks will be able to track the document to you photocopier. Apparently it is designed to catch crooks who counterfeit money on a photocopier, although it is hard to see how anyone call fall for fake photocopied cash.
News source: The Inquirer