Due to the lack of a railfan view on the IRT I could only get side shots on the Dyre line which really killed the quality. Not much more to say here so I'll just cover most things in the photo descriptions.
The full set of photos can be viewed here. I urge you all to go take a look at them.
First I rode through E180th interlocking to Bronx Parkway on the (2) Train. There I took pics of some of the E180th approach signals before getting on a southbound 2 train back to the E180th station.
Anyway, here is the 38L signal showing a Clear signal.
In the case of the 38L signal you just saw it only had one route therefore its second head only had a red placeholder lamp (with a call-on light below that). The 40L signal slightly down the tracks has a route into the yard so its lower head gets an additional yellow light for that route.
Of course E180TH intelrocking is most well known for its unique tri-headed IRT signals, which resemble some sort of strange black cast iron cactus. The IND/BMT style signals do not allow for more than two main-line routes in this fashion and therefore intelrockings have to engineered to always give trains a simple diverging or straight message. At E180TH they could just add an extra head.
E180TH interlocking is also cool for having this double slip switch.
All of this is controlled from the big US&S Model 14 interlocking machine inside E180TH tower, which is the last major electro-mechanical tower on the mainline IRT.