These codes will not work in posts or when writing the e-mail. The image will appear there when the e-mail is sent/received.
If you want an image to appear above the header (address area) of an e-mail, then use the following codes (using one set of "incorrectly" closed table tags after the opening HTML command, as shown below):
text (if any)
Rest of sig codes here
and the image will appear above the address area and the message/text of the e-mail.
This will put an image below header but above the email text. Put this after the closing