We don't see your numbers in the data sources in any specific currency.
But in your formulas you can add a prefix or suffix that will display the currency on your dashboard.
How to do it:
When editing a formula you'll see in the bottom of the page a prefix and a suffix box. In here you type the currency or text of choice:
Prefix - in front:
Suffix - behind:
The pre- / suffix can be any text of your own choice.