I just think that this sort of thing fluttering on my flag pole will give a much more visible trigger to the "blind cagers" of this world
It's a standard sort of thing that kite shops carry. My local one has closed and most of the online dealers seem to just advertise power kites etc. They might have something that'd work for you here.
They aren't difficult to make. Triangles, sewn staggered and then the ends sewn to a hoop such that the stagger converts to a gaping bulge. (Did that make sense?)
Alternatively, most kite things shops I've seen have had them or similar.
Lots of drag though - I used them where I wanted more drag than could be reasonably done with a conventional kite tail.