There is indeed a poster between platforms 4 and 5. It's been there some time. It replaced a previous version when the contactless area was extended to Virginia Water.
View attachment 182521
Image shows poster at Reading which states that contactless payment is not available on routes via Wokingham, or routes west of Reading.
That poster isn't immediately obvious at all. I had to think carefully what is meant by - "Contactless is not available [...]: Reading to Wokingham and Feltham/Gatwick"
To someone who's not familiar with the stations on the line, what on earth does that mean?
Between 'Reading to Wokingham' and 'Feltham/Gatwick'?
'Reading to Wokingham' as well as Feltham to Gatwick?
There is "to", "and", and "/".
Why not just write 'Reading to Feltham*/Gatwick'? *should be Virginia Water as mentioned above.
As an example, the LU Picc line goes from 'Cockfosters to Uxbridge/Heathrow'. I don't think anyone would say the line goes from 'Cockfosters to Acton Town and Uxbridge/Heathrow'?
As other people have mentioned above, I think the best method is to state where contactless IS valid at Reading, i.e. only Reading to Paddington. All other routes are invalid.
Another confusing part of the poster: the last sentence in the poster implies contactless is valid between Gatwick and Redhill on GWR.