….Stick a Bluetooth LE or equivalent transmitter on it. Even better if you can get GPS. Even more if you can get a low power cellphone chip.
Call this a node.
A node has a unique id. Nodes get stuck on objects in a non-removable way. So basically, you have a ThingID.
A ThingID periodically pings for any ThingIDs that are near it, and remembers what they are. In other words, it’s a small mesh network of ThingIDs that are near each other. If a ThingID near another ThingID goes away, they both remember it and timestamp it. Maybe you can use signal strength to triangulate and get more precise locations….