CHOAM, or the Combine Honnete Ober Advancer Mercantiles, is the organization in the Dune setting that financially controls all trade in the known universe. While the Spacing Guild actually controls international travel, CHOAM handles all the money. All significant wealth in the Padishah Empire is based on control of the stock, and holding directorship positions on CHOAM's board.
Because, y'know, the Great Houses are all trying to grift as much as they can. Which we here at Goblin Dynamics absolutely understand.
This flag is described in a single sentence near the end of Dune, when the Padishah Emperor raises the flag as "yellow... with a black and red circle in the center", to show that he doesn't care who wins, as long as economic considerations are maintained. In other words-
The spice must flow.