House flag of La Sambre
The company La Sambre, based in Antwerp, was named after the river Sambre (190 km), which has its source in the north of France, waters Maubeuge, then crosses the border, waters Charleroi and flows into the Meuse in Namur.
According to the Boone Scripophily website (offer no longer online), the company was formed in 1914 for shipping activities on Belgian internal waterways and on the Rhine; the company still issued shares after the 1944 financial reform.
The house flag of La Sambre, as seen on a share, is white with a red letter "S".