This is in today's business section:

http://www.washingtonpost.com/wp-dyn/content/article/2005/10/18/AR2005101801663.html

Quick take:  all color printers print a code unique to the serial number on
every page.

One of those great ideas like having a disinformation branch in the Pentagon
for the "foreign" press or having DARPA collect all available data on US
citizens.

While the desire to stop currency counterfeiters is commendable, this may
well be another over reaction with far reaching implications for rest of the
world and future generations.  While I am positive Dick Cheney would never
use this tool to track down someone who published pictures of war dead
arriving at Dover AFB, I would not put it past Putin or the Chinese to track
down people who published pictures THEY did not like.

And the printed code is unique to the printers serial number.  If you
registered your printer, or if the store tracks S/N on the invoice, then it
is only a couple phone calls.