They took orders from their customers, did the fiddly bits to actually make the trades happen and then took a small fee on every trade to pay themselves.
Taking a fee for every trade fired at an exchange would remove some of the haze that surrounds our market structures that have grown so esoteric that big trading firms must woo particle and quantum physicists to its fold.
The bank has hit on a less capital-intensive approach of expanding its corporate-fee business, but since much of this is trade-related it has suffered recently.
U.S. citizens are exempt from paying the fee as a result of a nine-year-old trade pact that requires that U.S. investors be treated the same as Singaporeans.