I doubt those are RFID tags. It's more likely they are security tags, basically a tuned circuit that loads a low level RF field when it's placed nearby. They are commonly used near the exit of a store and trigger an alarm if one passes through an RF field to indicate the goods it is attached to are not paid for. At the checkout, the tag is placed in a very strong RF field which fuses a link and breaks the tuned circuit. This stops the tag operating he exit alarm.
Brian.