Go to the SHIELD accessories app from the SHIELD TV home screen.
If you are actively using a SHIELD Controller, the SHIELD accessories app will report which controllers are connected and which one is "active" (in current use).
You can also rename each SHIELD Controller. Select the controller you wish to rename, and select "Accessory name". This name will stay with the SHIELD Controller, so if you connect it to another SHIELD device it will continue to be listed with the new name.