The semaphores used on trucks were much larger than Trafficators and were mounted to the outside of the body rather than disappearing into slots in the body. Also, the truck type, IIRC, were only on the drivers side and indicated right, left and slowing in the same fashion as an arm signal. They were, in fact, an extension of an arm signal, as an arm signal could not be seen past the load. Some were lighted, others were not, but had reflectors instead.
