Returns the ID of the plot style object associated with the layer record object (DXF 390) or OdDb::kNULL when the layer is not associated with plot style. This plot style is used when the PlotStyle property of an entity belonged to this layer is set to ByLayer value. The actual plot style can depend on the viewport in which the entity is rendered.

Specific Properties of Layers 

OdDbLayerTableRecord::plotStyleName() methods 

OdDbLayerTableRecord::setPlotStyleName() methods