Yellow signal of Upper side is analog sine wave about 9kHz.
Blue signal of Lower side is control signal for modern model railway. It is called DCC -Digital Command Control-. Multi trains on the same track controlled individually by this pulse signal of +- 20V.
I used DCC command "Stop and Turn On the Light" when I took tookapic.com/photos/130104. So I could take lighted headlights and signs during train stopped.