In article ,
Neil wrote:
Supposedly everyone who ever needs to read your card will eventually have a
handheld reader, although I haven't seen one yet. If they can't check your
card then they'll have to take your word for it that it's valid, as it's
hardly your fault that they can't read a ticket their own company has
issued!

I /think/ I've seen one on the GOBLIN. Or at least, it was a guard
with a new ticket machine (blue, rather than gray). I didn't notice
an oyster reader on it, but I was about half a carriage away.