This module operates all types of Semaphore Signals that are able to move. Don't use a cheap model with a fixed arm.
You can make your own signal from square or round PVC tube and other plastic parts and a brass ladder is also available on the web.
A servo is used to provide the activation via a "push rod" and the servo can be mounted above or below your layout. An under-board mounting bracket is available for the servo @ $3.50 extra. Ask for it when ordering.
A length a fine spring steel wire is provided with the module and it is connected between the signal and the arm on the servo.
You will have to work out which way to mount the servo to get the correct activation.
The servo operates very slowly so the signal looks realistic.
The module comes with a track-side IR detector and when the loco reaches the detector, the signal is activated.
The train can then advance.
After about 15 seconds, the signal returns to its original position.
The package contains the Semaphore Signal Module, Servo, IR detector for side-of-track with 4-core wire approx 1m long and 0.5mm spring steel push-rod 100mm long.
You need a 9v to 12v DC supply.  The module requires less than 100mA.