score:6
In all cases where the currency does not have a symbol, it is appended with its ISO code; this is also the case where the symbol is not standardized.
Wikipedia has a currency symbol entry where you can see various abbreviations used for currencies; note not all are symbols (a single glyph).
The general rule is, unless its a symbol it is always post-fixed:
In all international transactions, the ISO4217 code is used as this is what is supported by the main interchange systems and networks (like SWIFT).