Requesting the local authority solely to exercise discretion isn’t advisable, I would have challenged the PCN wording, as if they overlooked that in their written response to you, then you could have appealed on a ‘failure to consider’, then added that to the points of appeal. Without such, your case is risky because of its narrow scope on the points to challenge. From what I understand (correct me if I am mistaken), but it doesn’t sound like the LA have made any procedural improprieties, so an appeal would be on the basis of a collateral challenge only (an administrative element in the paperwork). An adjudicator’s interpretation on a legal point can vary, therefore I cannot say whether or not to appeal. If you require the wording checked on the Notice of Rejection then by all means let me know, if anything at least you have the PCN wording to challenge, while there might be a separate aspect to mention on sign placement (others may disagree).