There are 2 ways a user can validate if Unstoppable is enabled in your environment: 

Validating the Auto registering feature by pressing Ctrl+Alt+U keys on the keyboard.

If a user is not in the Unstoppable group, the Accessibility Dialog window will pop-up upon pressing Ctrl+Alt+U, as shown below: 

If a user is already a part of the Unstoppable group, the Accessibility Dialog window will not pop-up upon pressing Ctrl+Alt+U

Hearing the commands validity via screen reader.

Only users who are part of Unstoppable group or users registered through the Enable Accessibility feature will hear the screen reader announce the commands like Save for later, Watch, Create, Share, Space Tools, & Tools as buttons, as shown below:

Users who are not part of Unstoppable group or users not registered through the Enable Accessibility feature will only be informed that the focused item is a link.