I think it is a machining symbol to identify those surfaces (generally on cast, molded or forged parts) which are produced my machining operations. It indicates that material is to be provided for removal by these operations.
The machining symbol is not to be constructed as giving any indication of the surface finish quality requirement.
The machining symbol should be used only in the view in which the machined surface is dimensioned, unless the intent of the drawing is clarified by their repetition in other views or sections.