What does the signal indicate when it instructs to "stop and then proceed, prepared to stop within vision"?

The instruction to "stop and then proceed, prepared to stop within vision" indicates that the train must first come to a complete stop. This is a critical safety measure that ensures the operator can assess the situation ahead and respond appropriately. After stopping, the train is permitted to proceed but only with caution, ready to stop again if necessary, as it may encounter signals, hazards, or obstacles that are not immediately visible at full speed.

The requirement for a complete stop is essential in scenarios where there may be potential dangers that could affect the train's safe operation. Once the operator has stopped, they can then look ahead and make a more informed decision about continuing, ensuring they can halt if any risks are perceived. This instruction emphasizes the importance of vigilance and adaptability in train operation, reinforcing safety protocols.

The other options suggest different levels of speed or caution that do not align with the requirement to fully stop first. Safety is paramount in train operations, making the complete stop the only correct interpretation of this signal.