Hey Dorkenmore,
it is called Owner ID and is available in the sidebar when selecting an item. If you open the sandbox level and go to the little market in the middle, you can see how all items near the vendors are assigned to their specific vendor.
For editing multiple items at once:
1. select them all
2. confirm with the "load multiselected objects" button in the sidebar
3. edit the Owner ID field
Sincerely,
Kevin
