Hi Zack,
You might be able to use the javascript snippet widget to accomplish the stop signs that you want to do. You would have to write a script that insert that icon or changes the color of the group box. You would start with the snippet hidden with conditional visibility. Then when you run your validation, if anything was missed, you could use conditional visibility to show the javascript snippet to apply the script.
https://appstore.home.mendix.com/link/app/43096/Incentro-Business-Acceleration/JavaScript-Snippet
Another option would be the scroll to anchor widget, which will make it easier to see fields that are showing a validation feedback.
https://appstore.home.mendix.com/link/app/2583/Mendix/Scroll-To-Anchor
And the last option I could think of is to just show a simple pop up message that says they need make corrections. Maybe even add in the message which sections they need to visit and the number of fields they missed.
Hope this helps!