Comment by Terr_
That depends on whether:
1. You're looking for a very specific person.
2. You want to unconstitutionally punish somebody for free speech, and you don't care who, you just want to cheaply find a convenient victim.
In that respect, tracking-dots are an invitation to #2, since they don't really need much in the way of human labor-hours or focus.
Tracking dots can be used to confirm that a specific printer was used to print a specific page. However, going from only a serial number to finding the name and address of its owner is going to be very difficult to impossible. You might be able to track it down to the retailer, but if you buy your printer in person from a stack at Costco, nobody has any idea which printer has which serial number.