For users who have editing privileges on courses hidden from student content is displayed and in the main course content with a "Hidden from students" label.

In the course index the link is styled with a dimmed style, this style is used for locked content as well and dependant on the styling may not be very different from the links to unhidden and unlocked content.

In the breadcrumbs when a teacher is accessing the hidden content the link has a dimmed style.

Suggestion

To help identify and differentiate hidden content from locked and unhidden content add the hidden icon (eye with the slash through it) to the course links, links in the course content and the breadcrumb. The icon is used in many places to hide content or indicate that the content is hidden.

Also adding an aria tag of hidden to the content links would improve the way screen readers would recognise this content.