OK, the sign didn't face the road as it should do, but you parked in a marked-out bay so it is incumbent upon you to check for a sign with any possible restrictions on that bay. And the presence of a second sign for the bay is against you.
My view is you do not have a robust case to take to the adjudicators, but no harm in submitting representations based on the sign not facing the street. One never knows, they may shoot themselves in the foot in their reply.
