Well, so far I use the Hide command to toggle the hidden then objects, select those I want, and make them visible.
During this procedure, (when only the hidden objects are shown), there could be a popup text shown (HIDDEN OBJECTS) or similar.
When something is selected and 'un-hidden', then text would dissapear.

alternatively, you could show hidden objects, when pressing H, with a slight hue.

If text, i would be nice as an HUD object, just a floating text in the active viewport.
This could also work well wih an isolate command.