client = gdata.apps.emailsettings.client.EmailSettingsClient(domain=
    'yourdomain')
client.ClientLogin(email='adminUsername@yourdomain', password=
    'adminPassword', source='your-apps')
client.UpdateSignature(username='liz', signature=
    'Liz Jones - (+1) 619-555-5555' + 'Accounts Management, A&Z LTD.')
How do you change signatures using python gmail api?