This repo is a quick example on how to set up custom sign types on 1.18 fabric.
Created by nyuppo and dopadream with help from the Fabric discord server: https://discord.gg/v6v4pMv
This example assumes you know how to set up a fabric mod, work with mixins, and create models/blockstates for blocks and items. Textures are provided.
While textures for the boat item and planks are found under the example_mod namespace, the boat texture must be under the minecraft namespace.
Also, this example makes use of adding to a vanilla enum. While it works here and will work with any other mod that does the same thing, it is recommended to use Fabric-ASM instead going forward. Just something to keep in mind.