I remember using other office suites, of which I work mostly with the word processor and presentation apps, and they have some way to signal that an open file is not saved. For instance, one of them put an asterisk (*) right after the file’s name on the top bar.
The best solution I found used for that purpose is that of EditPad, whose Lite free version I’ve been using for years. To signal that the file the user is editing is not saved, it turns the file name background to red:
Is there a way to signal unsaved files in LibreOffice? TIA.