What should you consult to determine the indication of a signal you do not understand?

Answer: B — Item 19 of the System Special Instructions

Consulting Item 19 of the System Special Instructions is crucial because it specifically addresses signal indications and regulations unique to the railroad’s operating environment. This section includes detailed explanations and guidelines regarding signal aspects, ensuring conductors understand the full context and meaning of signals encountered during operations. The information provided here is tailored to the nuances of the railroad's practices and therefore more relevant than general information found in other resources. The employee handbook typically contains a wide range of policies and procedures but might not delve deeply into specific signal indications. The signal diagram provides a visual representation of signals, which is helpful but may not offer sufficient context or explanations for signals that are confusing. The safety manual covers safety protocols and guidelines but does not specifically focus on signal understanding, which is paramount for operational safety and effectiveness in the field.