minecraft-assets/data/minecraft/recipes/mangrove_sign.json

{
  "type": "minecraft:crafting_shaped",
  "group": "wooden_sign",
  "key": {
    "#": {
      "item": "minecraft:mangrove_planks"
    },
    "X": {
      "item": "minecraft:stick"
    }
  },
  "pattern": [
    "###",
    "###",
    " X "
  ],
  "result": {
    "count": 3,
    "item": "minecraft:mangrove_sign"
  }
}