Owned & worked for many print shops, advertising agencies, graphic designers, etc over the years. Said that just to make my next statement a little more credible. I'm CONSTANTLY using a (really cool) highly powerful magnifying ocular to scrutinize prints and I've used and been around just about every printer known to man and I have NEVER came across no crap like that. Occasionally there are defects, printing errors, ink splattering, misaligned printheads... a whole number of things but absolutely nothing that would indicate that these printers were printing some sort of secret message/I.D. Not saying it's completely out of the realm of possibility, just haven't came across it myself & I have butt-loads of experience.