The signature is separate from the rest of the email content, so it does not have any formatting currently applied.

Open a new Write message. Make sure there are no signature - a completely clear empty composing section. I suggest you press on 'Enter/return' key to create a blank line at the start as it ends up looking better and also allows you add anything just in case required.

Make sure you have the 'Formatting Bar' visible. 'View' > 'Toolbars' > select Formatting Bar'

Select all formatting even if already auto selected by default settings. Anything auto set up in default settings will not be good enough, you must select what you require even if it looks like you are just reselecting it.

• Select Arial font
• Type signature eg: Regards and name

• 'File' > 'Save as' > 'File'
• Choose where to save it. I have created a 'Signature' file in my Documents folder where I save all signature files and anything associated with them like images.
• Give the file a suitable name: eg Formal sig
• Save as type 'HTML'
• Click on 'Save'

Now you need to attach that file in Account Settings. see image below as guide

• Right click on mail account in Folder Pane and select 'Settings'
• Select : 'Attach the signature from a file instead'
• Clickon 'Choose' button
• locate the html signature file and click on 'Open'
• Click on 'OK'

Note: If user reads using Plain Text all formatting is stripped automatically.

While this was more than I expected... it worked perfectly .. Thanks for taking the time to solve that mystery for me.. I never would have figured that out on my own...

Good to hear all working as expected. Basically, you have used Thunderbird's Write window, which has easy to select formatting for html, to create a .html file. This means you did not need to know anything about writing html code. It is also a good method should you need to create more complicated signatures.

I've just located this article - if any one reading this question wants to use it. https://support.mozilla.org/en-US/kb/signatures

Additional info for anyone reading this question. If you want to have the ability to use more than one signature. eg: Formal signature, informal signature, signature specifically used to contact children etc. Create more .html files then use the addon to apply them when required. You can put a button on the 'Composition toolbar' or use 'Options' > 'Signature Switch' located on the 'Menu Bar'.

Addon extension called 'Signature Switch'

• https://addons.thunderbird.net/en-us/thunderbird/addon/signature-switch/
• http://write.flossmanuals.net/thunderbird/signature-switch/