Final answer:
When a railway employee signals you to stop at a crossing, you must stop even if no train is visible, ensuring safety and complying with the rules.
Step-by-step explanation:
If you are approaching a railway crossing and a railway employee is signalling you to stop, you should comply and stop moving and become stationary until you are advised it is safe to proceed. Railroad employees are authorized to ensure safety at crossings, and their instructions take precedence even if you do not see a train approaching. The proper action is to stop; slowing down or sounding your horn and attempting to cross could be dangerous and is not advised.