Simple method: Create a email which has the required signature and then save it as a 'Template' email in the 'Templates' folder. Then when you want to create an email using that signature, instead of clicking on Write, click on 'Templates' folder and double click on the stored email to open in a new Write message with signature already displaying. Alternative: You could use an addon called Signature Switch. https://addons.thunderbird.net/en-us/thunderbird/addon/signature-switch/ Please note : the author of this addon is not employed by Thunderbird and if you like the addon, the author would appreciate a donation to help maintain the addon.