Over the years I have sent my postcard artwork naked. It always bothered me that inkjet tracking marks would get put on the art side of the postcard. I wondered if putting the actual card on a larger surface would allow the card to escape the tracking depredations of the Post Office. :)
Checking out what dimensions were allowed and still remain the standard postage in price I made some test pieces and sent them off. From everyone who sent back a scan or photo of the card they received it appears the marks either do not get put on or they are put on the sabot part of the card. Wunderbar!! I have a number of pre-stamped international cards that will not get the sabot treatment but after that, all cards will get said treatment. If you get one from me, you can cut the sabot piece off and it I laid out the card properly (not always a sure thing with me!) the backside should be whole.
*not quite the dictionary definition of a sabot but we english speakers are notorious for corrupting language...