Removed the ObjectControl and added ( sub) to the name of the sub graph node

com.unity.shadergraph/Editor/Data/Nodes/Utility/SubGraphNode.cs

             }
         }
 
-        [ObjectControl("")]
         public MaterialSubGraphAsset subGraphAsset
         {
             get

com.unity.shadergraph/Editor/Drawing/Views/MaterialNodeView.cs

         {
             var subGraphNode = node as SubGraphNode;
             if (subGraphNode != null && subGraphNode.subGraphAsset != null)
-                title = subGraphNode.subGraphAsset.name;
+                title = subGraphNode.subGraphAsset.name + " (sub)";
             else
                 title = node.name;
         }