Train dispatchers are the air traffic controllers of the railroads. They control the movement of trains over large track territories.
Train dispatchers assign train symbols to indicate the train type, origin and destination of train and other information. Different railroads uses different train symbols. Knowing each railroad's train symbols help to make the model railroad operations more prototypical. I reread Stephen's 24 hours at Tower 17, Rosenberg report and trying to decipher all the 77 train symbols, both BNSF's and UPRR's.
By looking at each train symbols, I can now tell the origin and destination of each train type. It also give me an idea where each train originates and what it carries with it, and where it is going - loaded trains normally to ports in Texas or other States such as those in Long Beach or Los Angeles, California or New Orleans, Louisiana for handover to /from CSX.
Coals come from Wyoming for Smither's Lake Power Plant traveling over BNSF Galveston to Thompsons.
The train symbols also tell the type of commodity or product that BNSF and UPRR carry in this region. Grains and coals are BNSF main commodities while UP bends towards rocks (?) and intermodal between New Orleans and Los Angeles.
So, you will see actual* BNSF and UPRR train symbols used on Rosenberg Meet.
* I was told the BNSF train symbols have changed but since I am modelling 2004 period, train symbols in Stephen's report remained correct.