Steve wrote:

- Oxford Circus - snakes and ladders. I heard that this is supposed to
signify the confusion one encounters when changing from line to line here
(since there are three lines that intersect here).

Yes, to all of these

This is only since the refurbishment; after a fire I seem to remember.
It used to have three suitably coloured lines in roughly the right
direction, passing through a circle, representing the three lines
serving the station.

- Walthamstow Central - no idea.

I can't remember...

It's a wallpaper or fabric design by William Morris, who lived nearby.

When the line opened, a leaflet was made with all the original station
murals on it (Walthamstow to Victoria).

It was also printed as a poster; I remember seeing it at the old poster
shop at Griffith House. I don't know if it's still available at the
museum shop, but I doubt it.