This message appears when you manually install an update of VR Tourviewer without an included Oculus Signature for your device.
This is a requirement by Oculus for using the Oculus VR Utilities in Unity for apps not sold in the Oculus Store and installed manually.

This manual installation of VR Tourviewer with an APK file has been deprecated. Instead the app is now distributed with an Oculus Release Channel, click the link below to register so you will have access to VR Tourviewer from the Oculus Store.

You can get VR Tourviewer for Gear VR & Oculus Go here: VR Tourviewer for Samsung Gear VR & Oculus Go