This thread is calling me to get on board an old hobby horse.
When G-BNWW – CITY OF MARSEILLES eventually arrived in Paris, the local engineer claimed that the spelling was wrong and painted over the final S.
However Marseilles is one of those French cities like Dunkirk which has a separate English spelling and thus Marseilles, is the correct spelling in English as opposed to French. If the intention had been to have native language spellings of these cities, we would have had "City of Roma" and City of Athina" or indeed we could have alternatively had "Ville de Marseille".
Needless to say my protestations at the time fell on ears totally free of pedantry.