OP, the council's legal obligation is:
Traffic signs
18.—(1) Where an order relating to any road has been made, the order making authority shall take such steps as are necessary to secure—
(a)before the order comes into force, the placing on or near the road of such traffic signs in such positions as the order making authority may consider requisite for securing that adequate information as to the effect of the order is made available to persons using the road;
(b)the maintenance of such signs for so long as the order remains in force;
What we know is that when the school streets restriction is in force anyone other than an exempted class of vehicle/person is b******d if they get as far as the bridge in your photo: they can't turn left or right and these are the only options. Therefore, although there is a clear advanced warning sign - in your photo- this cannot be the only advanced sign, there has to be at least one other before the bridge and before Pembury Road.
GSV is no help, it's out of date.
Pl don't photograph any knee-high adverts, these aren't 'traffic signs'.
So, whether you came along Pembury to access Ruskin or turned in from the high street we need to know what 'traffic signs' are on the route.