Reply #12: I've been looking for confirmation of this story, and alas,

[atommom]

I found it. (I was sort of hoping it would turn out to be another urban legend...)

http://www.pcworld.com/news/article/0,aid,118664,00.asp

WASHINGTON--Next time you make a printout from your color laser printer, shine an LED flashlight beam on it and examine it closely with a magnifying glass. You might be able to see the small, scattered yellow dots printed there that could be used to trace the document back to you.

According to experts, several printer companies quietly encode the serial number and the manufacturing code of their color laser printers and color copiers on every document those machines produce. Governments, including the United States, already use the hidden markings to track counterfeiters.

Peter Crean, a senior research fellow at Xerox, says his company's laser printers, copiers and multifunction workstations, such as its WorkCentre Pro series, put the "serial number of each machine coded in little yellow dots" in every printout. The millimeter-sized dots appear about every inch on a page, nestled within the printed words and margins.

"It's a trail back to you, like a license plate," Crean says.

The dots' minuscule size, covering less than one-thousandth of the page, along with their color combination of yellow on white, makes them invisible to the naked eye, Crean says. One way to determine if your color laser is applying this tracking process is to shine a blue LED light--say, from a keychain laser flashlight--on your page and use a magnifier.