Beginning in the mid-1990s, many printer companies started incorporated hidden symbols and codes in every print job produced by their machines. This is known as a form of Steganography, which more or less means that documents produced by a particular machine can be traced back to the model, date and time that is was originally produced. This can then be used for a variety of reasons, ranging from criminal investigations to company audits of resources.
Most manufacturers will not mention this practice in their promotional literature. While the watermarks, patterns or text secretly embedded into a printed document may not be immediately visible, closer inspection will almost always quickly reveal the stamp of steganography on your documents. The reason this information is obscured is because larger manufacturers fear customer backlash over privacy concerns.
This subtle tracking of all your documents is usually done with color laser printers and some models of inkjets. Practically every major manufacturer of printers in the world has some form of it programmed into their machines. The initial claim was that it would curb their devices from being used to make counterfeit money.
Many consumers feel violated upon learning about this secretive practice and rightfully so. If you are buying a product you should be aware of anything and everything it is doing to your documents. Next time you set out to buy a printer, and would like to know all if its specifications, be sure to do a quick internet search to find out whether or not the machine will be tracking every single document you produce.