src/main/resources/assets/aether_legacy/recipes/skyroot_sign.json

{
  "type": "minecraft:crafting_shaped",
  "pattern": [
    "###",
    "###",
    " X "
  ],
  "key": {
    "#": [
      {
        "item": "aether_legacy:skyroot_plank"
      }
    ],
    "X": {
      "item": "aether_legacy:skyroot_stick"
    }
  },
  "result": {
    "item": "minecraft:sign",
    "count": 3
  }
}