The two-letter abbreviations for Swiss cantons are widely used , e.g. on car license plates and in the ISO 3166-2 codes ( with the prefix `` CH - '' , i.e. CH-SZ for the canton of Schwyz ) . The two-letter abbreviations for Swiss cantons are widely used , e.g. on car license plates . They are also used in the ISO 3166-2 codes of Switzerland with the prefix `` CH - '' ( ConfÅ `` deratio Helvetica , Switzerland ) , e.g. CH-SZ for the canton of Schwyz .