I got the impression that the Southern "target" style (similar to London Underground) lasted a significant length of time into BR days, and were not routinely replaced by a green BR "totem" (which I have always called the "double sausage") unless they were actually broken. Certainly the residual stations on the lines taken over by the WR at the end of 1962 had kept their targets right through the green totem era, and never got any brown ones either, right through to the post-1965 corporate image black/white era. And even then not for a long time afterwards.
The WR in contrast had replaced many signs with the double sausage. The old GWR had not put up a lot of signs on their stations anyway, not the one-per-lamppost SR approach. And I remember being astounded on my first ever trip from Manchester to Leeds, must have been about 1965. As soon as we left Standedge tunnel there were vivid orange totems, running in boards, timetable covers, everything, as the onetime North Eastern Region stamped its independence everywhere.