The purpose of a train symbol is simply to identify what each train is. In one way or another most train symbols will denote priority, commodity, origin location, destination location, and often date of origin.

In railroad terminology, train symbols are unique alphanumeric codes used by dispatchers and railroad staff to identify a specific train's type, origin, destination, and priority. Instead of just "the 9:00 AM freight," a train might be identified as Q326-25. In this example (used by CSX), "Q" indicates a high-priority intermodal or manifest train, "326" is the specific route number, and "25" represents the day of the month it originated. Other railroads like BNSF or Union Pacific use similar systems; for instance, a symbol like Z-WSPSTO would denote a high-priority "Z-train" traveling from Willow Springs (WSP) to Stockton (STO). These symbols allow the railroad to manage "train swells" and prioritize traffic; a "Z" or "I" (Intermodal) train carries time-sensitive cargo like UPS or FedEx trailers and will typically be given the "main iron" (priority) over a lower-priority "M" (Manifest) or "G" (Grain) train, which might be put "in the hole" (on a siding) to wait.