A while back, I would create a subtask in every project or folder called DNA (Determine Next Action) then any tasks in that project or folder were entered as children of the DNA task. So long as their was an uncompleted subtasks under the DNA task the DNA task was inactive but once all the tasks under DNA were completed the DNA task activated and I knew I had to review and create some more actions. I had a tab with a view of DNA tasks. If the view was empty I knew all my projects/folders had at least one next action.
I've since switched to using automatic formatting with several rules to present icons for different conditions. One such rule, Identifies projects that need next actions. Here are the conditions in my rule.
IsProject = TRUE AND
HideInToDo = FALSE AND
Complete = FALSE AND
HasIncompleteSubtasks = FALSE and
(Context does not contain >Suspended AND Context does not contain > Someday)
The task is a project, is not hidden in todo, is not complete, does not have incomplete subtasks, context is not >suspended and not >someday.
These tasks get a yellow warning triangle icon as a visual indicator that the project does not have at least one next action in it.
I also have rules for whether the subtasks are past due, due soon, or not past due or due soon. Helps zero in on where attention is needed during daily reviews.