It is possible to track printed documents back to their original printer or photocopier, based on a serial number that is attached to each print-out. The identifying mark comes in the form of white and yellow dots invisible to the naked eye, according to PC World. This means the government and printer companies can trace printed documents back to the individual machine it came from and the time and date it was printed, if the machine has that technology. Only the government and the printer companies know what the markings mean.

read more here: https://www.lawweb.in/2012/10/how-do-i-identify-printers-id-signature.html