The contract of deposit shall be in writing and signed by all individuals who have a current right to payment of funds from an account. The designation of an agent, or trust or P.O.D. account beneficiary by a depositor of a joint account without right of survivorship, or the designation of an agent by a depositor of a joint account with right of survivorship or by a depositor of a trust or P.O.D. account does not require the signature of a codepositor. A financial institution may insert such additional terms and conditions in a contract of deposit as it deems appropriate.