The problem with the requirement for signage to be 'adequate', is that it is subjective. Your 'inadequate' is a council's 'adequate'. So you have to convince an adjudicator that your view is correct. Each case turns on it own facts, there being no hard and fast rules that one can follow to prove 'inadequacy'. That said, a lot of appeals are won where the driver has to turn left or right into the restriction. At a junction, a driver must be alert to traffic and pedestrians at the junction, so without any advance warning of the restriction that alerts him not to attempt the turn, one can state the signage is 'inadequate'. HOwever, it is the adjudicator who decides, based on the civil law test of "on the balance of probabilities". That is why we always recommend appellants request a hearing at the London Tribunals, and never a decision on the papers.