Note: Extra fees might apply for Signature Required. Confirm here:
How to modify Per Order
You can change the Order Option on the order to enable Signature on Delivery. To do that on an individual order just expand the order (click the down arrow to the right of the Actions button) and then change the Signature on Delivery option in the Order Options to Required.
How to set as a Default option (applied to orders when they are imported)
You can also change the option for all orders by editing the default settings. Just go to CARRIERS on the menu and edit your MyPost carrier. Go to the DEFAULT SETTINGS tab to change the option.
Please note that AusPost charge an additional $5.50 for signature on delivery for international orders.