Aragorn säger detta i The Two Towers efter Boromirs död.
'I have not seen these tokens before,' said Aragorn. 'What do they mean?' 'S is for Sauron,' said Gimli. 'That is easy to read.' 'Nay!' said Legolas. 'Sauron does not use the Elf-runes.' 'Neither does he use his right name, nor permit it to be spelt or spoken,' said Aragorn. 'And he does not use white. The Orcs in the service of Barad-dûr use the sign of the Red Eye.' He stood for a moment in thought. 'S is for Saruman, I guess,' he said at length.
The Two Towers - Chapter 1, The departure of Boromir