What does this traffic sign indicate?

You answered correctly. This traffic sign indicates a cul-de-sac, also known as a dead end. It means that the road does not continue through, so any vehicles entering will have to turn around and exit the way they came. It is important to recognize this sign so you do not expect a through road or look for further exits ahead. This is not a sign for an underpass or a complete road closure for vehicles; it only informs you that the road ends ahead.