In the middle column, type a name for the signature.
The name appears in the Signature pop-up menu when you write a message.
In the right column (the preview), create your signature.
You can use the Edit or Format menus in Mail to change the font or layout, turn text into links, or check spelling. To add an image, drag it into the preview area.
If you want your signature to appear after the original text of messages you reply to or forward, deselect the “Place signature above quoted text” checkbox.
In the Mail app fill out and sign PDF forms.