California
Code of Civil Procedure CCP § 2030.250
(a) The party to whom the interrogatories are directed shall sign the response under oath unless the response contains only objections.
(b) If that party is a public or private corporation, or a partnership, association, or governmental agency, one of its officers or agents shall sign the response under oath on behalf of that party. If the officer or agent signing the response on behalf of that party is an attorney acting in that capacity for the party, that party waives any lawyer-client privilege and any protection for work product under Chapter 4 (commencing with Section 2018.010 ) during any subsequent discovery from that attorney concerning the identity of the sources of the information contained in the response.
(c) The attorney for the responding party shall sign any responses that contain an objection.