Did you know that most color laser printers leave tracking dots so that you can trace the type, model, serial number, date, and time when a particular page was printed?
According to research conducted by the Electronic Frontier Foundation (EFF) in 2015, most manufacturers of Color Laser printers and some ordinary Laser printers insert the so-called Machine Identification Code (MIC) with each print. According to sources, there are claims that the state authorities asked Xeorx, which is a pioneer of this technology, to install a monitoring mechanism in the earliest models to reduce the chance that the devices, unnoticed, will be used to counterfeit money.
Meanwhile, other companies have been required to implement a similar labeling system. There are already known cases in the judiciary where whistleblowers were caught only thanks to forensic analysis of documents they released to the public. They were probably caught for using their own printer to print confidential documents.
Reference to the list of printers for which they have confirmed the existence of the MIC code: EFF List
You can read an interesting research paper on this topic at Research Gate.
I personally tried to look for a print on my HP Color Laser printer, but I failed. I miss the UV lamp to check in enough detail. But I definitely plan to take a deeper look at this.
According to a Wikipedia article (Wikipedia), there are suspicions that the yellow print has been replaced by a subtle variation of laser power on more modern printers. More sophisticated equipment is now needed to read the black variation of the print.