It could just print the mac addresses of all the nearby wifi networks. One subpoena to google's mapping service and you know exactly where the paper was printed. Yay, surveillance.
Seems like a lot of data to print. I suppose just unique id would be enough. If the printer has access to wifi or internet connection in general (even through usb drivers) it can report the details.
Well, modern printers print with 100s of ppi, which on doing some maths suggest around 100 dot in a box of side 1 mm(in 250 ppi, most printers print with more ppi), enough for displaying 64 bit number with hash, even if it only works in binary mode. If more that just on/off can be detected, it can store much more.