Final answer:
The best action for a train operator who receives an unclear hand signal or lantern is to stop the train and seek clarification to ensure safety.
Step-by-step explanation:
If a train operator receives a poorly executed hand signal or lantern so that they are not positive of the meaning, the BEST action for them to follow would be to stop the train and seek clarification before proceeding. This is essential for the safety of everyone involved, including the train operator, passengers, and other personnel on the railway. By stopping the train, the operator can prevent potential accidents or misunderstandings that could arise from misinterpreting the signal.