Hi DaveW, I just checked mine and found a few with the same type of printers mark on them. I don't think they are common, but I would not call them rare. One thing I did notice was that it only occurred on the Piedmont 150 series and not on any of the 350 series. This was from a sample of approximately 250 cards of all 3 seies of Piedmont backs. Perhaps, there was a change in the printing methodology between the two series? It would be interesting to hear from other collectors.