The thread up yonder about the deprecated exonym Eskimo for the preferred endonym Inuit sent me searching for other kinds of ethnonyms (or demonyms). I ended up at an article in the German Wikipedia about the terms Ortsneckname (link) which is literally place-nickname (or perhaps topohypocoronym for the pedant completist). It's a kind of humorous nickname for the inhabitants of some place. This made me think of terms like Michigander or Hoosier. And it reminded me of a dictionary I once stumbled upon that opined that all toponyms had their origins in hydronyms.

Ceci n'est pas un seing.