The notice does not need to be signed. Depending on how the plan is set up, there may be other documentation that needs to be signed - an amendment - if it is a SHNE "maybe" or "not" with an annual change to "yes" when desired.
Then you inform the client that they need to get you whatever information is required for you to accurately calculate their benefit before the RBD if they want to avoid a disqualifying failure, and fines.