Once you are ready to set up your email signature, log into your Yahoo Mail account using a web browser. At the top right, click on Settings.
On the panel that opens up, click on More Settings at the bottom.
On the left menu, click on Writing email.
In the Signature section, ensure that the signature toggle is enabled for your email address and paste your new signature into the text box provided.
Click the Back to inbox button in the top left corner and then click to compose a new email message. Enjoy your new signature!