flagman

From flag +‎ -man.

flagman (plural flagmen)

1. A man who carries a flag, especially one used for signalling.
   • 1959 February, G. Freeman Allen, “Southampton—Gateway to the Ocean”, in Trains Illustrated, page 88:

     At the approach to Southampton Terminus, double track branches off to the left, runs alongside the platforms and then cuts across Canute Road on an open crossing under the protection of a flagman.