Signe Ida Katarina Hornborg (8 November 1862, Turku – 6 December 1916, Helsinki) was a Finnish architect. Possibly the first qualified female architect in the world, she attended the Helsinki Polytechnic Institute from the spring of 1888, graduating as an architect in 1890 "by special permission". She first worked in the agency of Lars Sonck, one of her notable works being the Signelinna (also known as Newanderin talo or Newander House) in Pori (1892). It was she who designed the facade of the Sepänkatu Apartment Building (1887) in Helsinki as it was not considered right for women to design entire buildings at a time when architecture was a man's profession.