Can an item be both an artifact and a reliquary?
I’d say yes. Buy Artifact and Reliquary separately, and simply apply those Background dots to one item. So, you can have an amulet that is a Level Two Reliquary and Level One Artifact, if you so choose. However, putting all your eggs in one basket may not be wise, as it’s an open invitation for a Storyteller to easily strip an overly dependent character of his portable arsenal. And keep in mind that a lost, stolen or destroyed item takes all the Background points you invested in it with it.