private Sign findSign(Inventory inventory) {
        if (inventories.containsValue(inventory)) {
            for (Map.Entry<Block, Inventory> entry : inventories.entrySet()) {
                if (entry.getValue().equals(inventory)) {
                    Block block = entry.getKey();
                    return (Sign) block.getState();
                }
            }
        }
        return null;
    }