Only thing it could be is an RFID chip used for tracking purposes... That doesn't mean you are being tracked though, they are so low powered that you literally have to be beside a scanner for it to activate and come up on the system.
When I worked at walmart and got a shipment of clothes in, instead of manually entering them into the inventory system, each article had an RFID chip in it, and we could just wave a scanner over the box once or twice and it would pick up each unique serial number that was tied to the piece of clothing and show in the system every last thing that was on that pallet... You will probably never know who made the chip, the ones found in clothes for our store didn't have any logos, just a little hard plastic button with the RFID serial stamped on it for visual purposes.
