In front office. It happens often that patrons come at the desk saying they didn't find a book in the library, that was actually only in a depot (so not freely available unlike books in central library).
The reason is that patrons check the shelf in CLC seeing the book status is "On shelf", see the call number, and don't verify the exact location (Central library, depot 1, depot 2, etc.).
It would be better to hide the call number for books in the depot and replace it by "Available on request".