I got done on the bridge at Berwick -upon-Tweed a few years ago.
Found a parking space at the end nearest the town, came back and found I had parking ticket, walked the length of the bridge to find a sign screwed to the bridge wall about 100 yards back up from where I parked that you could only read if you were bending down to read it.
Called my lawyer the next day, he said pay the fine, not worth the hassle and costs in time and money and the issues if you lose, which I will, he said.
Pay the fine and put it down to experience, if you lose as has been said the issues with credit scoring and possible higher costs are not worth it.
Am glad in some ways I don't drive any more.