Sales Order / Invoicing comments

Is there a way to differentiate between INTERNAL and EXTERNAL comments when entering a Sales Order?  We have some comments that are needed for our shop and shipping employees to appear on the Picking List and some comments that are for the customer and need to appear on the Invoice.  Now we are just deleting the lines that are not needed for the customer while invoicing but there has to be a better way.  Any ideas or input?