Transportation service provider (TSP) claims received by GSA or its designee must include one of the following:
(a) The signature of an individual or party legally entitled to receive payment for services on behalf of the TSP;
(b) The signature of the TSP's agent or attorney accompanied by a duly executed power of attorney or other documentary evidence of the agent's or attorney's right to act for the TSP; or
(c) An electronic signature, when mutually agreed upon.