@Junior posted:...the "coil" symbol shown above represents one relay. And the wiring diagram would need to be replicated for "each" coil (aka relay). So in the above example, the wiring diagram would be replicated 6 times for the 6 relays ("coils")....correct?
So there's no confusion, I'll answer a different question with a visual aid. 
The "original" signaling circuit as implemented by Chris used one 3PDT relay per 3-aspect signal head. I demonstrated the same functionality using two SPDT relays per 3-aspect signal head. It's just that you can buy these relay modules with 1, 2, 4, 8, even 16 relays on one board...which can save wiring depending on your layout geometry.
If you follow some of the links to earlier threads, you will see I recommend inserting a 5-cent resistor and 10-cent capacitor on each input to the relay. This helps demote signal light flickering or relay chatter when a consist enters or exits the insulated-rail section and there's only one or a few axles on possibly dirty track and wheels. If you have clean track/wheels and don't care about occasionaly flickering, then you can skip the resistor-capacitor combo and directly wire from the insulated-rail section to the relay input.
Note that for the eBay relay modules shown above, you do not actually directly drive the relay coil. If you are not using these relay modules, but instead directly driving a 12V DC relay coil, then let me know which relay you have and I might have more to say!
Also, as drawn in this diagram and the diagram you reference, I'm assuming a so-called "common-anode" LED-style signal head. Shown above is a signal head photo from eBay seller "we honest" who has been discussed many times over the years for their attractively priced O gauge signals and accessories. Their common-anode 4-wire RYG signal comes with a resistor so you can directly drive them with 12V DC.
