From the three e-mail clients from CPanel, only Squirrelmail has options for adding a signature to your e-mails.
To setup a plain text signature, login into your e-mail box, “squirrelmail”, click on “options”, “personal information”, notice the blank space near where is saying “Signature”. Copy/paste or compose your signature. All done.
From the bottom of the same page, notice “Signature Options”, select “Use Signature”. If you don’t, you will have to click on the “signature” button every time you compose a new e-mail.
You can use paragraphs when creating your signature, the “—” characters to separate paragraphs instead of the “hr” HTML tag.
For HTML signatures, from “options”, “display preferences”, try to locate an option called “email composition format”. If you don’t see it, it means that your squirrelmail client is not supporting HTML signatures.
Even if you compose a HTML signature and send a test e-mail on an address where you will receive the e-mail, you will see the code instead of a HTML signature, this includes Outlook Express, Gmail or Yahoo.
Finally, you can contact your hosting support team and ask them more about adding a HTML signature from squirrelmail, if there are more options for their respective squirrelmail version installed on the server.