The sign at Wimbledon also seems to suggest that you must touch the
pink validator if changing between tube and train, but as far as I can
see almost no one ever does. The confusion isn't helped by the fact
that there's yellow validators on the tube platforms, pink validators
just beyond the platforms, yellow ones on the ticket gates at the top,
and special tram ones on that platform - I think people have learnt to
ignore them unless they have to open a gate.