Banners at General Assembly: history?

Does anyone know when the first banners appeared at General Assembly, or Universalist General Convention, or at the Unitarian “May Meetings”?

I know the British Unitarians have these at their Annual Meeting, but who influenced whom?

I wonder if there’s an inheritance from trade union, women’s sufferage, and related reform movement banners (on either side of the Atlantic?)

If you know something, do add it in the comments.