No Index is an addon that allows moderators & curators to mark a discussion as noindex/noarchive:
This addon must be enabled by your CSM or Vanilla Support.
Once enabled, you will see an additional option when you click the Cogwheel on Discussions:
Once enabled, you will see an indicator that is has been marked as noindex:
You can also see this by examining the source code:
To reverse this action, simply click the cogwheel again and choose 'Remove Noindex'