These signs use the Wood Sign. Hold down the Custom Signs mod key while placing one.
To use this mod you need Content Patcher and Custom Signs.
Technical
If you want to complain or ask for help or help me test my mods, you can visit my Discord server.
A list of all my mods for Stardew Valley is available at https://www.nexusmods.com/stardewvalley/articles/895.