Here are "Bag Tags".
Or at least a photo of the package one may come in. These are a Tomy Gacha item, meaning you won't know which tag you get until you open it. There are 6 to collect including Sonic, Tails, Eggman, Knuckles, Shadow & a close up of Sonic's face. (Why not Amy, a Chaotix member or Blaze or Silver?)
See the notch in the edge? These may be meant to hold an identifier card of some kind that fits inside. While it says it's a 'bag tag', it's likely it could be used as a keychain unless they're huge. These have been sold in Australia, but they've also been seen in the Netherlands. Does anyone actually own one of these to see how big it is? (TODO: in collection of Hedgy, make a picture)