by traffic-light-man on Sat Nov 17, 2012 7:15 am
Yep, it's what Plessey came up with in the 1960s to replace written text "DON'T CROSS/CROSS NOW" and "WAIT/CROSS" lanterns to fall in line with the introduction of the X-Ways crossings (The trial for what is now the Pelican crossing!) in 1967 - and it became the standard from then on.
Why they didn't just use a standard tin housing size, I'm not sure.
If anyone's interested in earlier UK crossing signals, I can try and get something together!