Yeah so @Labob has hit the nail on the head. Essentially we have a really old file store that was imported from the old site and then merged with a load of inline uploaded images. This has been a really big issue with updating the site and requires me to manually configure the file store after each update. The site developers are releasing frequent updates which makes it harder for me.
So.. for the past 4 - 6 months I have been migrating away from that file store and moving the images to a more organised store. With hundreds of thousands of images that has taken a fair bit of time. I am now left with a load of 'bastard' images with no parents. These I have temp disabled to study the impact. It generally on the older posts and some signatures for people who have not updated recently.
As to how to proceed. If you could ideally re-upload your signatures then that would be the best issue. Depending on the impact will depend on what I do to fix them.