I found this information from IRS: https://www.irs.gov/pub/irs-pdf/i1099b.pdf
Box 1d. Proceeds Enter the gross cash proceeds from all dispositions (including short sales) of securities, commodities, options, securities futures contracts, or forward contracts. Show a loss, such as one from a closing transaction on a written option or forward contract, as a negative amount by enclosing it in parentheses
