- Log in to RoundCube.
- Select "Settings".
- Select the "Identities" tab.
- Select the email address you wish to add a signature to.
- Enter your signature here.
- Log in to Horde.
- Hover the mouse over the settings gear icon on the top menu, then hover the mouse over "Preferences", and click "Mail".
- Under "General", click "Personal Information".
- Fill in your signature in the designated field, then click "Save".