1. Open the Mail.app email client.
2. In the Menu bar go to Mail > Preferences > tab Signatures
3. Choose the Google Suite account and click on the button "+"
4. Name the signature and click in the blank field. Make sure to leave the box "Always match my default message font" unchecked.
Leave the Mail.app opened and open a new window in your browser.
5. Open CHROME and go to https://www.signaturesatori.com/app/user (Please, use Google Chrome, copy paste in Safari doesn't work for Mail.app.)
Fill or update information for your signature.
6. When you are finished, click on the button Save and Preview
7. In this modal window carefully select whole signature and copy it with CMD + C
8. Go back to Mail.app > click in the empty field and paste the copied signature with CMD + V.
Images are not shown due to a Mail.app bug. But don't worry, it should display just fine when it will be used in an email.
9. Select your new signatures from a dropdown of Choose Signature section.
10. Close the window with the settings.
Your signature is ready.
Something went wrong? Make sure you didn't miss these important steps.
1. The signature must be added as a part of Google account.
2. Make sure to leave the box "Always match my default message font" unchecked.
3. Always use Chrome to open your User page.