Do you want to save your notes as an image or as text?
Toby, my wife had cancer so we had to keep track of a lot of notes from doctors meeting. I built a FMGO app to manage all of this and to write notes with an Apple Pencil. I took notes two different ways. I used a keyboard app called MyScriptStylus. This app replaces the keyboard with a writing area that converts your writing into text in a field. This worked very nicely. The other thing I did was use an app like Noted Plus to write notes on a split screen. Note Plus can also convert the notes into text which can then be pasted into filemaker. I would also store the Note Plus PDF in FileMaker. Both of these worked well and had much more capabilities than trying to write notes in a signature box.