sig·nal·man /ˈsɪgnḷmən, ˌmæn/
  信號兵
  Sig·nal·man n.; pl. -men  A man whose business is to manage or display signals; especially, one employed in setting the signals by which railroad trains are run or warned.
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  signalman
       n : a railroad employee in charge of signals and point in a
           railroad yard