"GBG" meaning in Conventions internationales

{
  "categories": [
    {
      "kind": "other",
      "name": "Palindromes en conventions internationales",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Symboles en conventions internationales",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Conventions internationales",
      "orig": "conventions internationales",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_texts": [
    "(Automobile) (1924) Sigle de l’anglais Great-Britain - Guernsey."
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Lexique en conventions internationales de l’automobile",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Signe distinctif en trafic international des véhicules automobiles immatriculés à Guernesey, prescrit dans le cadre de la Convention sur la circulation routière de Genève de 1949 et de la Convention sur la signalisation routière de Vienne de 1968."
      ],
      "id": "fr-GBG-conv-symbol-Vn0PjyzV",
      "topics": [
        "automobile"
      ]
    }
  ],
  "tags": [
    "invariable"
  ],
  "word": "GBG"
}

{
  "categories": [
    "Palindromes en conventions internationales",
    "Symboles en conventions internationales",
    "conventions internationales"
  ],
  "etymology_texts": [
    "(Automobile) (1924) Sigle de l’anglais Great-Britain - Guernsey."
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "categories": [
        "Lexique en conventions internationales de l’automobile"
      ],
      "glosses": [
        "Signe distinctif en trafic international des véhicules automobiles immatriculés à Guernesey, prescrit dans le cadre de la Convention sur la circulation routière de Genève de 1949 et de la Convention sur la signalisation routière de Vienne de 1968."
      ],
      "topics": [
        "automobile"
      ]
    }
  ],
  "tags": [
    "invariable"
  ],
  "word": "GBG"
}