Hello GeorgesWare, I assume you are talking about Email signatures.

To add your signature on Thunderbird, click the menu button (which is located on the top right corner of the Thunderbird window) and click "Account Settings".

In Account Settings, navigate to Signature text and add your desired signature. After that, the next time you write an Email, your signature is then automatically added at the end of the Email.

Please refer to the images if you need additional context.

Hope it helps and if it does, kindly mark this answer as the solution (solved)!

Hello GeorgesWare,

Did the previous answer above manage to help solve your issue? If so, kindly mark the previous answer above as the solution (solved) to help others with similar problems in the future! If not, please report back so I can help!