Aspects are displayed visually by the signal itself. The type of signal determines how the aspect is physically shown to the train crew.
Color light signals display aspects by illuminating specific colors of light, such as red, yellow, green, lunar white, or other colors. These lights may be arranged vertically, horizontally, diagonally, or in other patterns, and may be steady or flashing.
Semaphore signals display aspects by the physical position of a movable arm or blade. A horizontal arm may represent one aspect, while an angled arm may represent another. At night, lights are used so the aspect can still be observed by the train crew.
Position light signals display aspects using patterns of illuminated white or amber lights. A vertical pattern, horizontal pattern, or diagonal pattern can each represent a different aspect.
Searchlight signals display aspects through a single lens that projects different colors, such as red, yellow, or green, depending on the internal mechanism or control system.
Indications are not directly displayed as words on the wayside signal. The signal displays the aspect, and the train crew interprets that aspect according to their training and the railroad's operating rules.
The process has two steps. First, the signal physically displays an aspect. Second, the train crew observes that aspect and applies their rulebook knowledge to determine the indication.
The railroad rulebook or timetable special instructions define the relationship between each aspect and its indication. This allows crews to know the required action for each signal display.
Some modern cab systems may provide additional visual or audible reminders related to signal information. However, with wayside signals, the primary display is still the aspect, and the crew remains responsible for knowing the meaning of that aspect.