What signals a train to resume normal speed after running at a reduced speed?

The option that signals a train to resume normal speed after operating under a reduced speed is the resume speed signal. This specific signal is designed to indicate to train operators that they can return to their regular speed limits after having complied with previous restrictions. It serves as a clear directive that the conditions allowing for a full-speed operation are now met, thus eliminating any ambiguity for the engineer regarding their speed.

On the other hand, while the clear signal and proceed signal may also indicate that it is safe to continue, they do not specifically address the transition from a reduced speed back to normal speed. The speed limit signal, in contrast, typically provides a speed restriction rather than guidance on resuming normal operations. Therefore, the resume speed signal is the most accurate choice in this context, as it directly communicates the ability to return to standard operational speed.