When isocurves of surfaces are displayed in Rhino the isocurves which are also knot curves and divide spans are not distinguished from other isocurves. In another thread @Lagom noted:
Something similar, perhaps the ability to set different widths and colors for knot curves in display modes, would be very usefult to users who care about how many spans a surface has and where the knot curves are located.
Currently in the V9 WIP there is a test command TestShowKnots which does this for selected objects. Perhaps an option could be added to make this automatic for all surfaces and polysurfaces.