Sauron and elf-letters

[Telchar]

Gandalf about the inscription of the One Ring:

‘No,’ said Gandalf, ‘but I can. The letters are Elvish, of an ancient mode, but the language is that of Mordor, which I will not utter here.

Legolas about the S-rune on the helm of the orcs fallen before Boromir near Parth Galen:

'Nay!' said Legolas. 'Sauron does not use the Elf-runes.'

So...?