* "Passengers must not cross the line" ... sign at a station (Farnborough North) with no way from platform to platform except by the level crossing. Oh - and the sign is at the level crossing!
I think you are being a bit harsh on that sign. Safety instructions have to be short and clear, and that usually precludes being legally or logically rigorous.
For this standard sign I would prefer "Danger! Do not cross the line here" as meeting that criterion better. True, at Farnborough North the place they want you not to cross (by going down the platform slope) is the same as where they want you to cross (going round by the crossing gate, so passing the lights and a barrage of notices), so it does look odd. The obvious answer there is to add a sign underneath with an arrow to the right and "Use the crossing".