HYMNE À MERMOZ. (ampersand pound sign 192 semicolon produces capital A grave). Why shouldn't they be used? The word is mis-spelled without the accent.

Umlauts and a few others offer real problems. Ö without the umlaut mark means that an "e" must be added after the "O" when the word is put into English; Peña must be spelled Penya if the tilde is left off. These are just two of the rules for transliteration into English that must be followed in printing.
Cañon is one that offers no problem since we have the equivalent word canyon, but many don't have direct equivalents.