Signals Notebook: Is there a way to prevent experiment 'Sharing' between users?

You can disable 'Sharing' in general with the help of 'User Roles' by following these steps:
    1. Log into Signals Notebook as an administrator
    2. Navigate to Configuration > User Roles
    3. Click on the 'Author' tab
    4. For the 'Standard User' role, remove the check from the 'Share' box

This change will remove the 'Sharing' button from top right corner for all standard users (or custom user roles if chosen). Administrators will still see the option to share.

If you wish to use security polices to restrict sharing at the group level, please refer to the article Signals Notebook: How does "Read Dependent Share" privilege work in Signals Notebook.