Sales Order # Placeholder in Email Template for SHipment Notification

Sales Order # Placeholder in Email Template for SHipment Notification

I need to add a placeholder field in the Shipment Notification that references the Sales Order #. While this field is not listed with the available placeholders, the sales order # is referenced in the Shipment module.

We want this field to be referenced when the customer is notified of their shipment.

Any ideas?  Thanks.