Выражение встречается в следующем контексте:
To facilitate price setting on the market, a reference price for
gold, the so-called “London fix”, is set twice daily (at 10.30 am
and 3 pm). Settlements on the market are organised in a similar
way as on the international currency market via accounts in various
banks. The standard size is a “London Good Delivery Bar”.
The settlement currency is normally US dollars.

Очень похоже на принятое обозначение.

Заранее спасибо