Keyham stop boards. Presumably in case an HST▸ has to call if making a substitute stop after a preceding local service has been cancelled.
Thanks for that suggestion, willc!
Interestingly, as both Bedminster and Parson Street have luxuriously long platforms (compared with Nailsea & Backwell!), the same situation could apply if, for example, the 1753 from
BTM▸ to Taunton was cancelled and the 1822 picked up the pieces, so to speak?
It has happened, by the way: I remember being on an HST that actually stopped at Parson Street to pick up passengers abandoned by an earlier service. It was such a unique situation (then) that everyone was absolutely amazed, and impressed, that it had happened!