We've seen a lot of cases in Oxendon Street where people didn't see or understand the taxi plate and I think we once had a technical challenge to the signs and road markings but I think that was scuppered.
The clutter with the extra suspension sign is worth a go on its own but unlikely to be accepted by Westminster.
The contravention is 'stopped on a taxi rank' but it's a no waiting not a no stopping restriction but wording can be changed to 'waiting' for the same code so maybe something in this.
I'll have a check.