Just since the book, as far as I know-- just an author's whim. Nothing more.
'O' isn't a Bible or anything, it's just a meagrely decent novel-- albeit with a ground-breaking theme.
Oh, sure, I get that. I wonder what inspired the author to use that symbol? It does have many meanings in different cultures, and there are many different ways to depict the symbol.
And I think "meagrely decent" is an excellent way to describe that book! I thought it was ok, but read it a long time ago. Maybe I'll give it another look sometime.
Hmmm ... that gives me an idea of another thread I wanted to start!