This should unlock when you reach rank 25 in any of the trading companies and buy the relevant promotion, Gold Buccaneer in the Gold Haulers or Merchant Officer in the Merchant Alliance (I don't yet know the rank in the OoS). This is for buying the rank from the trade company representative NOT for buying the badge from the clothing shop.
This didn't work for me with the Gold Hoarders but unlocked okay as soon as I reached rank 25 with the Merchant Alliance.