The internal comments are only seen by you and the email shopper field is seen by the customer when you hit the save/send button.
To create signatures, which are saved responses, you can click on either the manage comments or the manage signatures links and then on the "add" button.
The manage comments and manage signatures is the same pop up so you can create for both there and use for either.
The saved signatures will then show each time you hit the "manage" links.