The signal on the left is displaying the clear aspect, which means proceed. The signal on the right is displaying the diverging clear aspect which means "proceed on diverging route not exceeding prescribed speed through turnout." Union Pacific rules.

This signal is displaying the advance approach aspect, which means: "Proceed prepared to stop at second signal. Freight trains exceeding 40 MPH must immediately reduce to 40 MPH. Passenger trains may proceed, but must be prepared to pass the next signal not exceeding 40 MPH. When signal governs the approach to a control point with a 40 MPH turnout speed be prepared to advance on normal or diverging route. When the next signal is seen to display an aspect more favorable than APPROACH or DIVERGING APPROACH, the requirement to proceed prepared to stop short of the second signal is no longer required." Union Pacific rules.

This signal is displaying the approach aspect, which means: "Proceed prepared to stop before any part of train or engine passes the next signal. Freight trains exceeding 30 MPH must immediately reduce to 30 MPH. Passenger trains exceeding 40 MPH must immediately reduce to 40 MPH. When the next signal is seen to display a proceed indication, the requirement to proceed prepared to stop no longer applies. Speed may be resumed once leading wheels of train have passed (next) signal." Union Pacific rules.

The signal in the center of this photo is displaying the approach diverging aspect, which means: "Proceed prepared to advance on diverging route at next signal at prescribed speed through turnout." Union Pacific rules. Note: The lower signal head on this particular signal does not have a green light, from the bottom up the colors are red, lunar, and yellow (amber).

This signal is displaying the diverging advance approach aspect, which means: "Proceed on diverging route not exceeding prescribed speed through turnout and be prepared to stop at second signal. Freight trains exceeding 40 MPH must immediately reduce to 40 MPH. Passenger trains may proceed, but must be prepared to pass the next signal not exceeding 40 MPH. When signal governs the approach to a control point with a 40 MPH turnout speed be prepared to advance on normal or diverging route. When the next signal is seen to display an aspect more favorable than APPROACH or DIVERGING APPROACH, the requirement to proceed prepared to stop short of the second signal is no longer required." Union Pacific rules.

This signal is displaying the diverging approach aspect, which means: "Proceed on diverging route at prescribed speed through turnout prepared to stop before any part of train or engine passes the next signal. Freight trains exceeding 30 MPH must immediately reduce to 30 MPH. Passenger trains exceeding 40 MPH must immediately reduce to 40 MPH. When the next signal is seen to display a proceed indication, the requirement to proceed prepared to stop no longer applies. Speed may be resumed once leading wheels of train have passed (next) signal." Union Pacific rules. Note: The lower head on this signal has four lights; from bottom to top they are red, lunar, yellow, and green.

This signal is displaying the approach restricting aspect which means: "Proceed prepared to pass next signal at Restricted speed, but not exceeding 15 MPH. When the next signal is seen to display a proceed indication, the requirement to pass next signal at Restricted speed no longer applies. Speed may be resumed once leading wheels of train have passed (next) signal." Union Pacific rules.

This signal is displaying the restricting aspect which means: "Proceed at Restricted speed, not exceeding prescribed speed through turnout when applicable." Union Pacific rules. The color of the lower light is lunar. A flashing red light is also used for this aspect.

This signal is displaying the stop aspect which means: "Stop before any part of train or engine passes the signal." Union Pacific rules. Note: The number of red lights can range from one to as many as three.

This is a single light "vertical color light" signal head. Please don't confuse this with a searchlight signal. The size and shape of the visor makes this one a "Darth Vader" type.

This is a two light "vertical color light" signal head. The colors, from bottom to top are either red and amber (yellow), red and lunar or red and green, depending on what is needed at a particular location. This style of signal head, with one large visor over all of the lights, is commonly called the "Darth Vader" type.

This is a three light "vertical color light" signal head. The colors, from bottom to top are red, amber (yellow), and green. There are some exceptions to this, for example you might see a signal head with red, lunar, and amber. This is a "Darth Vader" type.

This is a four light "vertical color light" signal head. The colors, from bottom to top are red, lunar, amber (yellow), and green. This is a "Darth Vader" type.

This is a triangular color light signal, commonly referred to as a tri-light signal. The color arrangment for this type of signal is typically red on the bottom, green on the left and amber (yellow) on the right, or green on the right and amber (yellow) on the left. Other light arrangments are possible. This signal has protective screens installed over the lenses, which suggests that it has had problems with vandalism in the past.

A signal that has a number plate is a permissive signal. This means that when the signal displays all red, it is showing the restricted proceed aspect which means: "Proceed at Restricted speed." Union Pacific rules. A signal without a number plate is an absolute signal and when it displays all red, that is the stop aspect.