Trade Dividends are received when in a wing with someone who makes a profitable trade, so long as you are in or outside to the station where goods are being sold. They are vouchers for a payment of credits, awarded by starports to encourage traders to group up in the system.
They may be handed in at any starport in the system, via the Starport Services Menu → Contacts → Local Security Office.
All wingmen in the group get a 5% bonus of the commodity's profit being sold.
Formula: Profit Per Ton * Amount Sold * 0.05 = Trade Dividend