Add protection support to signs

mods/default/nodes.lua

@@ -650,6 +650,10 @@ minetest.register_node("default:sign_wall", {
 	end,
 	on_receive_fields = function(pos, formname, fields, sender)
 		--print("Sign at "..minetest.pos_to_string(pos).." got "..dump(fields))
+		if minetest.is_protected(pos, sender:get_player_name()) then
+			minetest.record_protection_violation(pos, sender:get_player_name())
+			return
+		end
 		local meta = minetest.get_meta(pos)
 		fields.text = fields.text or ""
 		minetest.log("action", (sender:get_player_name() or "").." wrote \""..fields.text..