ambari/ambari-web/app/assets/data/settings/motd.json

{
  "href" : "/api/v1/settings/motd",
  "Settings" : {
    "content" : "{\"text\":\"You are using test mode\", \"button\":\"\", \"status\":\"true\"}",
    "name" : "motd",
    "setting_type" : "ambari-server",
    "update_timestamp" : 1454428666251,
    "updated_by" : "admin"
  }
}