This name appears in the Signature pop-up menu when you write a message.
In the right column (the preview), do any of the following to create your signature:
Edit your text: Click Edit in the menu bar to paste text, turn text into links, and check spelling and grammar.
Format your text: Click Format in the menu bar to change the font and color, change text alignment, and add lists.
Add an image: Drag an image 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.
Go to the Mail app fill out and sign PDF forms.