To create a signature under Opera Mail
- Click on the Menu button select "Mail and Chat Accounts".
- Select any of your accounts and then click on the Edit button
- This shall open up the "Account Properties" window
- Select the "Outgoing" tab and click on the "Edit Signature" button
- You finally have access to the Signature editor.
- Select "Use HTML Formatting" for more options
- Once done check "Apply current signature for all accounts" and click on the Save button.