Here's a little rabble-rouser from TechNews Daily:
"A research team led by the Electronic Frontier Foundation (EFF)
recently broke the code behind tiny tracking dots that some color
laser printers secretly hide in every document.
"The U.S. Secret Service admitted that the tracking information is
part of a deal struck with selected color laser printer manufacturers,
ostensibly to identify counterfeiters. However, the nature of the
private information encoded in each document was not previously
known.
" "We've found that the dots from at least one line of printers
encode the date and time your document was printed, as well
as the serial number of the printer," said EFF Staff
Technologist Seth David Schoen.