Thunderbird – setting up a Signature Open Notepad (Start\All Programs\Accessories\Notepad Type up the Signature there as you want it to look. Save to C:\Program Files\Mozilla Thunderbird and name the saved file Signature.txt Now go into Thunderbird to Tools\Account Settings. On the first screen there, you will see a check box named “Attach this Signature”. Click to check it. Click on the “Choose” button. Navigate to the Mozilla Thunderbird folder, locate Signature.txt and double-click on it. You should now see that path in the box. Click OK at the bottom of the Account Settings box.