A-road cantilever sign
A green sign suspended over the road from a post on the left with a diagonal arrow pointing up and left, and the following text.
Alconbury Weald; The Stukeleys; Non-motorway traffic; B1043 [Hollow square diversion symbol].
The Stukeleys sound like a folk band who tour pubs.
Hang on a minute - "non-motorway traffic"? That can only mean...