A character in Mahou Shoujo Lyrical Nanoha A's.
She appears in neither the previous series Mahou Shoujo Lyrical Nanoha nor the alternate universe story Triangle Heart, but appears in Mahou Shoujo Lyrical Nanoha StrikerS. Signum is the leader of the Wolkenritter (German for "Cloud Knights"), a creation of the Book of Darkness.
Signum's weapon is a chain-link whip sword called Levantine, and as a magical creation, she has no familiar. She is named for the Opel Signum, much like characters of Magical Girl Lyrical Nanoha are named for cars, and her device appears to be named after the mythical sword Laevateinn. As per the other Wolkenritter, she has no last name.
She is voiced by Shimizu Kaori (Japanese) and Bailey Chadwick (English).