I think you could achieve that with a personal tag. But, I admit that personal tags were much better put to that purpose before they were created by default.
It's very likely that we will return to the old system of two tags and a community tag soon. As before, if the author so desired, she could make one of the tags a personal one.
We have also envisioned a version of saved posts where you could create categories for them. We call them archives. thenewgreen has been lobbying for them for years. :)