Fortunately, Mac OS X Mail makes it easy to insert simple text links — all you have to do is type the URL —, and you can turn images into links comfortably, too.
Add Links to Signatures in Mac OS X Mail
To insert a link in your Mac OS X Mail signature:
- Type the URL.
- Mac OS X Mail automatically creates links for all web site addresses starting with "http://" or "www".
To link text or an image in a Mac OS X Mail signature:
- Click in the signature you want to edit in Mail preferences' Signatures tab.
- Press Command-A.
- Now press Command-C.
- Press Command-N to create a new message.
- Click in the message body.
- Press Command-A again.
- Press Command-V.
- Highlight the text or image you want to link.
- Select Edit | Link | Add... from the menu.
- Enter the desired address.
- Click OK.
- Press Command-A once more to highlight all text.
- Press Command-C.
- Go back to the Signatures preferences window.
- Make sure the entire signature text is still highlighted.
- If it is not, click in the signature and press, yes, Command-A.
- Press Command-V.
- Close the Signatures window.
- Close the New Message window as well, not saving the email as a draft.
Note that such rich-text links will not be present in the plain-text equivalent Mac OS X Mail automatically generates for recipients who prefer to read their mail in just text.

