An anonymous reader writes: The EFF has posted a nice little guide decoding the grid that is printed by the Xerox DocuColor series printer. The FBI and NSA use this to keep track of certain groups, like Greenpeace, here in the US. The article itself only covers the DocuColor series printers, but the EFF warns that this maybe used by other printers as well. Very interesting read, and also very scary knowing that whatever we print can possibly be tracked with exact date and times and the serial number of the printer used. Enjoy!