These signs have a commonality in presentation. They show the "No Waiting" symbol, that all motorists are supposed to know, but when loading is also barred, there is no symbol for that, so the words "No Loading" are added. YOur photos of the sign shows the symbol, plus the words "No Parking", as well as "No Loading", so I'm somewhat at a loss as to what you expected to see on a temporary suspension sign.
For me, you are bang-to-rights and the discount is your best option unless the PCN contains fatal errors of content making it void. To check for such errors, please post the back of the PCN.