Perfect description in every way.
So, literally, it's a Jeep thing. You (nor I, nor anyone) wouldn't understand.
I really do think it's great that different car cultures do different things to become a community. After all, despite the fact that all Jeep products are total ******tboxes when stock, people buy them and buy them and buy them. And yes, of course, they do so to become part of a community. I can't poop on them, even though I think it's silly, because everyone deserves to be happy and all that. The GX community does its own things.
In short, people leave these little duckies on Jeeps they see that typically used to mean "nice Jeep, random guy!" and now they just put them on every Jeep they see. It's a physical manifestation of the Jeep wave.