It's all on paper. Just a fancy say to say a train name or number. NS uses its own system. 100-series are general freight, 200-series are intermodal and automobile trains, 300- and 400-series are general freight again. 500-series and up are unit trains. NS also uses letters interchangably with numbers because of the limitations on their computer system. As an example 20A is just another intermodal just as 218 would be. A number first in the symbol signifies an extra train or local. I3W is a second section of 23W and B98 is a local. It's a bit deeper than I can explain in the space here, but it's a start for you!
