In the Netherlands we have three-letter citynames like 'Urk', 'Oss', but in my opinion they should not be allowed when used wihout additional data: provincename and countryname. So valid locations would be 'Urk, Flevoland, Nederland' and 'Oss, Noord-Brabant, Nederland'.
So in general (Netherlands) citynames should be qualified by provincename and countryname.