It is quite amazing sometimes, how computer users are spied out these days.
Although it was reported already several times, watermarks on print outs of color laser printers are a rising problem, since the prices of these printers are constantly  declining and thus are more common even in private households.

The official justification for the watermark, which the printers print on each sheet of paper, was that it should prevent the usage for producing faked money.

Well, one might ask, if it would be by any means be likely to use a laser printer to do this, especially in terms of the costs. As far as I know, most printers would refuse to print any banknotes.

Many printers print a for the human eye invisible code out of yellow spots on each sheet of paper. This code contains even the serial number of the device.

This way anonymous printing is impossible. Well, of course, no one has anything to hide, but nevertheless there may be occasions, when one would like to print a document, that does not secretly contain the manufacturer of the printer, the serial number, date, time and so on.

Well, anyway, you should not print any political fliers on your own color laser printer