core/homeassistant/components/mqtt/icons.json

{
  "services": {
    "publish": {
      "service": "mdi:publish"
    },
    "dump": {
      "service": "mdi:database-export"
    },
    "reload": {
      "service": "mdi:reload"
    }
  },
  "triggers": {
    "_": {
      "trigger": "mdi:swap-horizontal"
    }
  }
}