“Trading-Marks” are scrips issued by the Golden Wheel, a Continent-wide merchant association, which can be traded in for a large quantity of a specific bulk resource. Marks are in high demand from the various nations, much more so than the more magical resources, simply due to how important food, steel, and lumber are to a nation’s economy and security compared to the materials needed to fashion a single magical item or a dozen potions.
During the last two Churnings, the Golden Wheel has managed to either get a trader into Veilguard or negotiate to have one of the residents of the town act as their representative, and this newest Churning is no different. You can seek out the Golden Wheel’s representative within Veilguard to trade coin for Marks, or Marks for coin, though it’s worth remembering that supply and demand may radically change the prices on offer either way.