Naomi-Mom-Chris

I'm fairly new to the whole geocaching scene, so my question might be one that's already been answered in the past, or just a stupid question all together But I figured I'd give this a shot. I've been looking into the whole travel bug thing, and was looking at what designs/styles a person could pick up to send out into the world. One of the ones that I came across was these Vehicle Static Cling/Decal/Magnet Travel Bugs. It says they come with the dog tags, so clearly there is something that you could go out and put into caches. But I don't completely get what the purpose of the item is that you put onto your rig. Is this just a way to showing that you are into Geocaching? Was just curious. Thanks for any input/answers you can swing my way!