What is a symbol starting with the letter “O” from the book The Catcher in the Rye?

Holden is suspicious of others and has a difficult time using empathy to put himself in their shoes.

“What really knocks me out is a book that, when you’re all done reading it, you wish the author that wrote it was a terrific friend of yours and you could call him up on the phone whenever you felt like it. That doesn’t happen much, though.”
― J.D. Salinger, The Catcher in the Rye