Themis was an ancient Greek goddess whose image may have been adopted as the symbol of Justice commonly known as the "Lady of Justice." The Lady is typically pictured as blindfolded, holding a sword in one hand and scales in the other.
Themis later evolved into the Roman goddess Justia. may have been based on Maat, the Egyptian goddess of harmony and order.
Themis and the Lady of Justice have been discussed several times on the Law-Lib listserv. You can retrieve a wide range of images by searching Google Images. For more information, see the article Representing Justice: From Renaissance Iconography to Twenty-First Century Courthouses and/or the book, Representing Justice (Yale University Press), both by Judith Resnick and Dennis Curtis.