From the link provided by Barbara Tomlinson of The National Maritime Museum
The house flag of The Broken Hill Proprietary Co. Ltd, Melbourne. A rectangular flag divided diagonally into red and blue by a white stripe from top right to bottom left. Inscribed on the stripe is 'B. H. P.' The flag is made of a wool and synthetic fibre bunting. It has a cotton hoist and is machine sewn. A rope and toggle is attached.
The Broken Hill Proprietary Co. Ltd was a major conglomerate based in Melbourne whose principal interest was mining. It entered shipowning in 1927. The company has now merged with Billiton Ltd and is known as BHP Billiton Ltd.