That's a splitting distant signal. They were quite common at one time but then fell out of favour for a while. While there are a few modern examples around now, the one south of Perth is the last 'old' one that still survives.
A splitting distant signal doesn't have the same function as a feather, and both can coexist as elements of the same junction signalling arrangement. The feather (or alternative form of route indication) is displayed at the junction signal itself, whereas the splitting distant signal gives advance routeing information on approach to the junction signal.
There are photographs of the Perth splitting distant signals (outer and inner signals)
on this page of my website.