Thank you Moin & Dan for responding and pointing me to the components. I will check them out. I expect they, along with Gated Topic Category, will work to accomplish the objective of restricting visibility & access to Categories/Topics.
I think it would be simpler and cleaner to have a new Display Category permission and link it to the Signup page like what happens when an anonymous visitor or logged out member clicks on Reply for a Topic within a Category that only has the See permission. This functionality would then be in the Core so no issues with components.
Regards