Currencies are given prefixes and suffixes for certain types of currency variations.
The only prefix we use is "X". The ISO uses an "X" when a currency is used across international borders. The West African Franc has been assigned the symbol XOF by the ISO and the SDR the symbol XDR. Consequently, XEAS is used for the East Africa Shilling.
The X prefix is also used for historical currency systems that were used in multiple geographic regions. The German Convention Thaler has been given the symbol XDCT because it was a monetary system used throughout Germany, but for which there were many local variations.
We also provide a number of generic suffixes that can be used to differentiate between government creates versions of the national currency. The most commonly used suffixes are:
Countries that attempt to fix their currencies against another currency often find it difficult to maintain the link. Consequently, black markets develop. Since black markets reduce the government's profits and control over the currency, the government introduces special rates for imports, exports, financial transactions, tourism and so forth. These "official" market rates usually differ from both the black market rates and from the official rates for the currency.
Using suffixes helps to differentiate between black market rates on the South African Rand (ZAFB) and the South African Pound (ZAPB). It also allows us to differentiate between the black market rate (ZARB), the financial rate (ZARL), and 3-month Forward rates on the South African Rand (ZARF3).
Most currencies have been traded on the black market, and most developing countries have had special rates for imports, exports and noncommercial or financial transactions. Because the reader can easily recreate these four-letter currency codes, we have not included these four-letter codes in our currency histories, unless the currency variation existed independently of the parent currency, or the ISO had assigned a code.