A Travel Bug, or any item trackable on geocaching.com is a game piece. People purchase them and send them out in the hopes that they will continue to travel far and wide collecting stories and photos along the way.
There is never a need to trade anything when taking or leaving a TB/trackable. You should not take a cache trade item and leave a Trackable in it’s place, since the trackable is not “swag”. If taking “swag” from a cache, you should trade up, trade even or don’t trade at all. If taking a TB, log it as soon as possible, and always try to log in the logbook in the cache that you took it. (This way, if you do forget to log it, someone else can check the cache and find out where it went.)
They are identified by a number – which may be engraved on them or on a ‘tag’attached to the item. Don’t confuse trackables with normal ‘swaps’ in a cache. You can’t keep trackables – always move them along if you can.