What does the title Bat Chain Puller of the song by captain beefheart means?

A bat chain refers to the chain that hangs down from a signal post on a train line. The signal device that was pulled down was called a bat and different bats had different colours to signal the train driver as to the condition of the track ahead, or whether the train could proceed,etc.

The bat chain puller was the person who set the signals for the approaching train according to track status reports received by telegraph.

The song BCP probably metaphorically refers to the fact that this job is obsolete in the world of train spotters in this automated world.