Yes, it's usually written 20 USD (or 20 GPB, or whatever the currency is).
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
GPYFor example, in the financial industry the currency code comes before the number, in my experience. There are suggestions in some places that there may be a BrE/AmE difference.Where I used to work (California, USA) the currency code was placed before the number, so I am not aware of any BrE/AmE difference.