Thanks! I'm surprised more rail enthusiasts haven't delved into the signalling side of things, given that they are likely the third-most public interface with railroads and up until recently many steam-era survivors existed. The loss of "Overhead 377" in Tehachapi has likely stimulated interest in the historic value of signals and such infrastructure and many museums have started collecting them, as well as restoring them to operating shape.

Also, one thing about SP crossing signals that I'm surprised hasn't been mentioned yet--from the 1940s onward (perhaps earlier?) SP installed the oldest railroad-exclusive crossing bell, the US&S Model 15A, en masse on its system. The uncommon peaked rainshield/housing and its lower-tone, syncopated ringing make it a railfan favorite, gaining the "Teardrop Bell" nickname for the former attribute. A few of these still survive on the NWP between Windsor and Willits and hopefully will survive re-activation of the line. SC&MB appears to be keeping its three on the La Selva - Santa Cruz stretch as well.

Here's one in Cornellius, Oregon for spotting reference: