Which of the following is a condition that must be met for the policyholder's assignment to be valid?

A valid assignment of an insurance policy typically requires the written consent of the insurer. This condition exists because the insurer must be informed about who is receiving rights and responsibilities under the policy. An assignment generally involves transferring benefits or rights from the original policyholder to another party, and without the insurer's approval, the insurance company might be unable to manage the risk appropriately or may have concerns regarding the creditworthiness or insurability of the new policyholder.

Written consent ensures that the insurer has the opportunity to assess the implications of the assignment, as it could change the risk pool or affect the terms under which the policy was underwritten initially. Consequently, it creates a formal record that keeps the insurer's understanding of who is covered under the policy up-to-date.

The conditions mentioned in the other options, such as notarization, proof of premium payment, or filing with the state insurance department, are generally not standard requirements for assignment validity in most jurisdictions. These measures could be relevant in different contexts or situations, but they are not fundamental to establishing a valid assignment as the written consent from the insurer is.