Hmmm.. is putting USD before the number very common in the US or other countries?
Currency symbols are a nightmare across different publications/industries. Standards are all over the place. Here are some common ways that you will see in different places. I'll stick to USD for the examples.
Normally, I would recommend using one of the following:
My preference there is (usually) for the top 2, though I prefer the bottom 2 for less formal usage. The top 2 are generally nicer to use with decimal places. e.g. USD $123.45.
The 3-character ISO scheme is the easiest to use. Using the actual symbols is a good idea as well when writing, though in OpalCalc I'd imagine that it wouldn't be needed as typing currency symbols can be difficult.
''There are various common abbreviations to distinguish the Canadian dollar from others: while the ISO currency code CAD (a three-character code without monetary symbols) is common, no single system is universally accepted.
And that's the real problem.
Local standards aren't very useful for non-locals. This makes the ISO system easier to use for broad/international audiences.
Taking a page out of the cryptocurrency ecosystem, they use schemes that mirror the ISO standard (for the most part), e.g. BTC vs. DOGE, which is an exception with 4 characters.