Signal

Signal. General term for railway mechanisms that are at least partially-lighted. Major forms include color-lighted, color-position, position, semaphores and signal board signals. The term can be restricted to mainline usage though it is also extended to specialized indicators (switch, point and shunting devices especially). It would appear that Signal at times is an umbrella term for any railway safety aid. Major components include the housing or case, optical assembly (lamps and lenses), hood, backplate (background, backboards or baffles), signal masts (and in some instances signal bridge and ladder).