Thunderbird client, because it has set up its own account before, so open the login directly.

Click "Account Settings" on the right to open the "Account Settings" dialog box.

There is a signature text field in the middle of the Account Settings dialog box. Edit your signature according to your own needs. Then click OK.

In this way, when we create a new email, the signature will exist in this email by default, so we have finished using mozilla.

Thunderbird sets our email signature.

You can also select an attached file (text, HTML or picture) as a signature (such as a picture) in the "Account Settings" dialog box, select a signed picture from the computer, and click "OK" to save after setting.

In this way, when we create a new email, the picture signature will be displayed.