If you can a lit a fire, the engine driver can spot it from far--it should be fairy big in size + have control over the fire. And if you have vehicle turn the lights of the vehicle on the spot where you want the train driver to see---
Your vote on this answer has already been received
How can I bring a red cloth to be used as a flag in emergency???? I'd rather run backwards against the approaching train waving my hands sideways to gesture to stop! I am sure the motorman can see me clearly through that distance and understand my sign!