Exactly! (subject to these being the signs)
If the junction of Henniker and Buxton with Leytonstone is a vehicle entrance into what the map shows as zone S, then as a minimum the sign which applies to your direction of travel (the one on the left) must be 'S', but it isn't, it's SNW with S on the reverse.
The sign on the right is optional or recommended depending on the width of the road, but it cannot substitute for the sign on the left.