It is a rainbow version of the treble ampersand. Stuart made this particular rainbow version, but he didn’t make the original symbol. He’s the artsy one.
Polyphony is a musical texture that has multiple distinct voices/melodies happening at the same time.
This is like our brain. I imagine that is a relatable plural thing, though.
Perhaps try to read about more stuff on our site or from other plurals. Reading people's personal experiences with it instead of general overviews may help you to better understand it.
The idea of plurality may seem far-fetched, but it has been scientifically proven to exist through brain scans. At least, DID has been.
There in an unreleased study that did brain scans on tulpamancers that could provide evidence in their favor.
We also have a study that compares endogenic plural's dissociative experience scale scores to traumagenic plurals. Check it out here: Origins of Plurality and Levels of Dissociation