core/homeassistant/components/fritzbox/icons.json

{
  "entity": {
    "climate": {
      "thermostat": {
        "state_attributes": {
          "preset_mode": {
            "state": {
              "holiday": "mdi:bag-suitcase-outline",
              "summer": "mdi:radiator-off"
            }
          }
        }
      }
    }
  }
}