It's not possible to tell from the frontend if you're viewing a hidden mod.
Perhaps a "top bar" element that says something like the following could be added:
This mod is hidden, which means it won't display in searches, and the Mod Manager will not display any view/download count or logo for it. A developer could chose to hide their mod for any number of reasons. Perhaps the mod is a library mod and not intended to be viewed directly, or maybe the developer doesn't want to develop the mod any more. Check the mod page for more information.
It's not possible to tell from the frontend if you're viewing a hidden mod.
Perhaps a "top bar" element that says something like the following could be added: