Step 1:
Open your browser and log in to Yandex Mail. In the top right, click the Settings cog and then click the Personal data, signature, picture button.

Step 2:
Near the middle of the screen, click on the yellow Add signature button.

Step 3:
Paste your email signature into the provided text box. Once done, click the Add signature button.

Step 4:
Your new email signature is now installed! Test it out by composing a new email to make sure it looks correct.
Yes! Now it worked!