Make the locked sign use a nodebox like the normal sign

[Amaz1]

Pretty much what the commit message says. I didn't rename the sign texture, like was done for the default one, because afaik, nothing uses this texture apart from this mod.

[davisonio]

:sparkles: https://github.com/CraigyDavi/Craig-Server_game/commit/1d40e1ef0981ff63b9e07a1356ab0a15f7e7b396