Prior to the installation of radios on Santa Fe freights, a visible wig wag signal was installed on the cupola of many ATSF waycars (what the ATSF called their cabooses). This signal consisted of a disc mounted in the top center of the cupola. The opposite end had a similar disc mounted, and both were operated by a hand crank from the same seat in the cupola. When originally introduced, these signals were painted like a bull's eye with a white or yellow center surrounded by a dark blue ring. There was a single light mounted in the middle for night time signalling. By 1943, the color of many of these signals was changed to reefer orange for better visibility.
A larger style wig wag (29-3/4") was introduced in 1940, which was a perforated disc. The perforations lightened the disc and reduced wind resistance. The entire disc was painted either reefer orange or yellow, and had both a red and a white light that were centered, and were on the side of the signal that faced the locomotive. These signals were mounted on the right side of the cupola as you faced it from either end. Note: the lights on the signal faced the locomotive and also the cupola. The side of the signal away from the cupola was painted the same color as the lighted side. Care was always taken so that the wig wag did not block the windows when in its resting position.
Radios began to arrive in the 1950's and the wig wags were slowly phased out as the radios became more reliable. Some actually survived until the late 1960's. The signals from the wigwag were only two. A straight up signal meant stop the train, and a side to side motion was the "highball". At night the lights were used with red for stop and white for the highball signal.
This detail can be easily scratchbuilt using styrene and brass rod. I have attached a drawing so that these unique signals can be scratchbuilt and added to your model.
