Returns a format mask for negative currency format.
Example of what can be returned:
($#,##0.00) (US on MacOS X)
-$ #,##,##0.00 (India on MacOS X)
-#,##0.00 $ (Icelandic on MacOS X)
Note that "$" symbol, "-" symbol, "," symbol and "." symbols are only placeholders for the actual symbols that should be queried from the CurrencyFormatter class.