D&RG 1924 Rule Book has the following rule:
221. A fixed signal must be used at each train order office, which shall indicate "stop" when there is an operator on duty, except when changed to "proceed" to allow a train to pass for which there are no orders. A train must not pass the signal while "stop" is indicated, whiout a clearance card. The signal must be returned to "stop" as soon as a train has passed. It must be fastened at "proceed" only when no operator is on duty.
Operators in changing the position of the train order signal from "stop" to "proceed", must do so when the change can be seen by the engineman.
. . .
Where a three-position semaphore is used, the arm indicates "Stop" when horizontal; "19 train order for delivery" when at an angle of 45 degrees; and "Proceed" when in a perpendicular position. (See illustration)
Where a two-position semaphore is used, the arm indicates "Stop" when horizontal; and "Proceed" when in a perpendicular position. A yellow flag by day, and in addition a yellow light by night, displayed on the semaphore mast, when semaphore indicates "Stop", will indicate "19 train order for delivery." (See illustration)
End of quote; following the rule is illustrated in color two and three position semaphores and the Newton. Semaphore blades show black to the rear and red to the read side. The Newton shows only a red blade (I presume the white had been removed by 1924 as referenced elsewhere in this thread) Yellow lense shows at 45 degrees on 3 position; for two position and Newton yellow flags and lights are shown. Both upper and lower quadrant semaphores are illustrated hence, the terms used are horizontal and perpendicular.
