What does the O stand for?

Via wood s lot, Todd McEwen deconstructs Cary Grant’s suit in North by Northwest:

This is what’s ingenious about this picture, at least as far as the SUIT goes—Cary’s able to travel all over the country in just this one beautiful suit…. It’s so well cut you can’t tell if he’s even carrying a wallet (turns out he is). Here’s what he’s got in that suit! He goes all the way from New York to Chicago to the face of Mount Rushmore with: a monogrammed book of matches, his wallet and some nickels, a pencil stub, a hanky, a newspaper clipping and his sunglasses—but these are shortly to be demolished when Eva Marie Saint folds him into the upper berth in her compartment. (Really this is a good thing, because Cary Grant in dark glasses looks appallingly GUILTY.)