2) This symbol indicates a KPI which is a calculated measures you could create in Power Pivot or SQL Server Analysis Service. When you import the data to the Power BI Desktop, it may look like a Traffic Signal indicator.
I think it is inappropriate to mark this question as "answered" because it gives a wrong impression that there is an authoritative source explaining FIELDS List icons. I understand that you cited links to community questions and answeres, however, they are not authoritative and are not in one place.
When the Power BI team updates the documentation, please let me me know so that I can mark this as "answered".