You mean between a home signal and distant signal?
Home signals have a flat ended, red arm with a red stripe and red and green lights, Distant signals have a fishtail end, yellow arm, a black stripe and a red and yellow light.
I think Distant signals were used when there was a large distance between two Home signals, and Home signals were used the most. I'll see ifI can find some more info for you, as I'd like to find out more myself.
A distant is a warning signal that gives the driver advance notice of the state of the home signal. The main difference beyond appearance, is that the distant can be passed if it is on or off.
It's confusing. I don't know if I set up my signals right then. I'll look when I get up in the morning or after I get home from class. Then I'll post my pictures. You can look up Eastland Rocket Progress & Eastland Rocket the first in the screenshot and the second surveyors. I think I'll need figure out how to set up signals when tracks are diverging. don't know of any RR's that use double signals on single or double tracks when there's no siding, yard entrance, etc. Usually it's bi-directional signals. Would love to explain more but I'm getting tired.