I found this interesting concept of "Movement By Staff System" in a Bessemer & Lake Erie Railroad Employee Timetable No. 81 from 1934.
Movement by Staff System
7--No train or engine will enter the Mercer, Bairdford or Indianola Branches without the staff, or train order to do so, unless protected in both directions as prescribed by Rule 99
A staff lettered "Mercer Branch Staff" is located in a box at switch leading to Mercer Branch at Mercer Junction. The possession of this staff by enginemen will authorize a movement from Mercer Junction to Mercer and return.
Main track switch at Mercer Junction by be left open while first class trains are using Mercer Branch.
A staff lettered "Bairdford Branch Staff" is located in a box at the north end of west storage track at Curtisville. The possession of this staff by enginemen will authorize a movement from Bairdford Junction switch to Bairdford and return.
A staff lettered "Indianola Branch Staff" is located in a box at the junction switch leading to Indianola Branch. The possession of this staff by enginemen will authorize a movement from Bairdford Junction switch from Deer Creek to Indianola and return.
Staff boxes must be kept locked.
Harry