You can access your RoundCube webmail at http://yourdomain.com/webmail, or via cPanel -> Email Accounts -> More -> Access Webmail.
After that go to Settings -> Preferences -> Composing Messages. Once there you need to configure the following options so RoundCube will attach a signature to your emails:
- Compose HTML messages to Always
- Automatically Add Signature to Always
You can edit the signature itself via Settings -> Preferences -> Identities. You can either choose the default identity or create a new one.
Under the Signature section check the box next to HTML signature and enter the desired information in the Signature field. You have two options to add an image to your signature:
- You can use the Insert/edit image tool in the Signature field. In this tool you can upload an image from your computer, or specify the image URL location (e.g. http://yourdomain.com/image.jpg).
- Alternatively, you can drag and drop the image URL from your browser to the Signature field in RoundCube.
Finally save the changes, and the image of your choice will appear when you compose your messages.