Wis. Stat. § 182.24: Transfers from joint tenants.

If any security issued by a corporation, whether or not organized or created under the laws of this state, is registered in the names of 2 or more individuals who are named in the registration as joint tenants, then any bank, broker, issuer, transfer agent or purchaser for value, acting either within or without this state in connection with a sale, exchange, transfer, redemption or retirement of such security, incurs no liability by treating the interest created by the registration as a joint tenancy and, if one or more of the named individuals is deceased, incurs no liability by treating the survivor or survivors as the owner or owners unless the bank, broker, issuer, transfer agent or purchaser for value has actual knowledge of a contrary adjudication under s. 867.04.