Licensing with NS, as these two railroads NS owns a portion of as well. Apparently though, if you contact DTM on facebook he'll send you the brandings.
Erie Lakwana is the only one thru Norfork Southern, while NS owns some part of Conrail, the logo itself is still trademarked by the CSAO (Conrail Shared Asset Operations) which DTG doesn't have a license for (The Heritage unit doesn't count). And the last time DTM sent something for approval from NS, it was an Erie Lakwana U34CH, which never got approved, which is why that's unbranded.
