The obligation on the council is:
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;
The scooter was parked next to the sign, IMO it could not be missed unless it wasn't there.
And as regards 'wasn't there', we weren't but the driver(s) was/were. I don't know when the scooter was parked only when you said it was..and you posted that it was parked 2 days after the 19th(the date on the sign)so the sign was there, or was it? The council's records will show when it was erected.
If both were parked before the single sign was erected, then it's immaterial in which direction the driver(s) went, there was nothing to see. And if you could claim that neither driver used the car subsequently, then that's it.
Don't lie about when the vehicles were parked, your defence needs to be the best possible based on the truth.