My initial thought was that this could be handled by the “global” icon in the header like we do for custom sections…
…but I held off because we’re planning on removing the title of that top section and would need to find a new place for this indicator.
For now I think this should help:
Here I’m showing the “Make this section public and visible to everyone” checkbox like we do in custom sections, but it can’t be deselected. On hover/tap a tooltip appears to clarify that this section’s content is always public.