Apparently, the Hanging Sign for Netherwood from MoreCraft is still bugged. Was using Supplementaries 1.1.11.

This should hopefully be the correct JSON file.

{
  "parent": "supplementaries:item/hanging_sign_template",
  "textures": {
    "0": "supplementaries:blocks/hanging_signs/morecraft/hanging_sign_front_netherwood_mc",
    "2": "supplementaries:blocks/hanging_signs/morecraft/hanging_sign_details_netherwood_mc"
  }
}

Found out that it was because the JSON file uses the wrong folder.

Also, the hanging sign placed on the world still has broken texture but the post does use correct texture.