I have seen this query come up before and it's something that certainly warrants consideration.
Where I've seen this done, customers have done several things: Either report on the incident ticket associated with the asset, capturing the fact that it has been stolen, or extend the list of status reasons (which I guess one might call a small customization).
Has anyone else out there seen similar/alternative approaches?
Creating a new status would be a major customization. You would have to add the new status to *Status and Z1_Status and update the corresponding workflow. You would probably also have to update Status transition mappings and filters.
Update the Status Reason field and adding a value may prove to be less work. You still have to update the two fields/menus and their supproting workflow. But there is less dependent workflow.