I just bought Papership for macOS and iOS and use it with Mendeley to annotate all my sources of information for a thesis I am working on.
Since I started using Papership though I feel that it could definitely benefit from some kind of visual cue to let you know which documents you have already annotated in your library.
Like you show a blue dot to indicate if a document is unread it would be really very useful to show which of your documents in list view have been annotated. This could be shown by putting a yellow dot somewhere in the document title.
I've attached a mock up to show you what I mean.
If you could add this I think it would definitely improve upon an already useful app.