Make it easy for us to identify items that are shared or are being shared with you by adding an icon to the vault list mode.
How you handle/use a vault item is influenced (absolutely in certain circumstances, such as editing them) by whether you are sharing it with someone or it is being shared with you.
e.g. I'm tidying up my humungus list of items in my vault to make searching more effective. When I come across an item that is shared with me, I am unaware of this until I try to save my edits and it tells me... "ERROR: This shared item can only be edited by its owner. To change it, recreate it in your own vault."