The standard accounting way is always to show negative numbers in parentheses. Where does this practice come from?
For example, this cash flow statement use parentheses indicate negative values:
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I'd love to see if someone can find a convincing origin story for the practice, but I believe it became adopted simply because parenthesis stand out more than a negative sign.
Think of a hand-written ledger or balance sheet, an errant dot of the pen could look like a minus sign, or a narrow column could leave too little space for the minus sign to be noticeable. Parenthesis are deliberate and easy to spot while scanning a sheet, so no idea who was the first to do it, but it was effective and caught on.