That’s fascinating. If i recall correctly, some printers, eg xerox machine, intentionally leave identifying marks on printed documents too, allowing someone to trace where the documents originated.
https://en.wikipedia.org/wiki/Printer_tracking_dots
Printer tracking dots, also known as printer steganography, DocuColor tracking dots, yellow dots, secret dots, or a machine identification code (MIC), is a digital watermark which many color laser printers and copiers produce on every printed page that identifies the specific device that was used to print the document. Developed by Xerox and Canon in the mid-1980s, the existence of these tracking codes became public only in 2004.
There’s a rumour that Mossad have a similar code, which when scanned by an airport luggage scanner, will cause the scanner to wave the item through.
