The first two letters of the code are the two letters of ISO 3166-1 alpha-2 country codes ( which are also used as the basis for national top-level domains on the Internet ) . The third letter is usually the initial of the currency itself . The first two letters of the code are the two letters of ISO 3166-1 alpha-2 country codes ( which are also used as the basis for national top-level domains on the Internet ) and the third is usually the initial of the currency itself .