This post describes a method for tagging text that is quite effective. The style highlight feature can be made as prominent as you like, and can be hidden entirely via View ▸ Text Editing ▸ Hide Markup for when you don’t want to see them at all. But of course the main advantage is being able to select all styled text and copy and paste it into a list somewhere for review.
This is a problem akin to making an index, which is not something Scrivener can do.
It can, as we’ve recently been discussing in this thread.