Cruceristanueva

We have booked a Forward facing deluxe penthouse on the Dawn (under the bridge), and after having watched videos where I could see a sign at the door that says “do not open while at sea”, or something like that, I am concerned now. So can’t we use the balcony during sailaway?? Does that mean that we can only use the balcony while at port? It’s a British Isles cruise.