If you are familiar with html, the signature can be edited for color, font etc. directly in the Signature text box in Account Settings. Otherwise, create a signature in the message composer and save it as an html file, and attach it:

https://support.mozilla.org/en-US/kb/signatures#w_signatures-stored-in-files

Thanks for your reply. Must have easy formatting option like Microsoft Outlook provide us in Signature & for email. This feature make Mozilla Thunderbird more user friendly. Other thing look goods.