Negative values display in a currency field

As indicated, the feature enablement for multi-currency does impact the display style. It changes system currency fields from using parenthesis to minus signs when displaying a negative number.

While multi-currency is not enabled, this display is controlled by the company locale settings.

For example, USD displays as (2000) while French Euro locale displays the same number as -2000. As previously stated though, once multi-currency is enabled, these locale specific changes are overridden.

See also:

Set Your Currency Locale

Enabling Multi-Currency

Supported Locales