What is the '¤' character?

This is the currency sign

A currency sign is a graphic symbol used as a shorthand for a currency's name.

Also from Currency (typography):

The currency sign (¤) is a character used to denote a currency, when the symbol for a particular currency is unavailable.

The symbol is available on some keyboard layouts, for example French, Danish, Norwegian, Swedish and Finnish keyboards, because it is used in business applications.