settings.py

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'HOST': 'localhost',
        'NAME': 'db',
        'USER': 'root',
        'PASSWORD': '',
        'OPTIONS': {
            'charset': 'utf8mb4',
            'init_command': 'set collation_connection=utf8mb4_unicode_ci',
        },
    },
}

shell output

$ ./manage.py shell
>>> from django.db import connection
>>> cursor = connection.cursor()
>>> cursor.execute("show variables like 'collation_connection'")
>>> print cursor.fetchall()
((u'collation_connection', u'utf8mb4_general_ci'),)