Log into your Webmail dashboard and choose the RoundCube option.
From the RoundCube dashboard, click on the Settings option in the upper right corner of the screen.This brings you to the RoundCube Settings screen.
Locate and click on the Identities tab. You are now on the Identities list screen.
Find and click on the desired identity in the left hand panel.
Clicking on the identity brings up two tabs in the right hand panel. Click on the Signatures tab. If you wish to use HTML in your signature, simply click the HTML Signature checkbox. This will cause the Signature field to change over for HTML allowing for special formatting.
Enter your desired custom signature in the Signature field.
Once entered, click on the Save button located underneath the tabs.You have now created your new email signature!
Adding images to your signature file
Upload the image either on your hosting account or on an image-sharing site.
After that you need to access your mail account and go to Settings.
Go to Preferences -> Composing Messages. Once there you need to set Compose HTML messages to always.
Open the link to the image you uploaded in your browser and repeast steps above to access your Signature file in HTML mode
Click on the image you wish to attach to the signature and drag it to the field called Signature.