This sign is used as an indicator of pregnancy. The sign was first described by French physician Etienne Joseph Jacquemin in 1846, but it was James Read Chadwick who drew attention to it in a paper he published in 1887. Although he credited Jacquemin for the discovery, Chadwick's name became associated with the sign.
Of course with easy lab and over-the-counter tests to confirm of pregnancy, it is now of very little clinical usefulness.