Before signatures, there were seals. In antiquity, beautifully carved gems were mounted onto rings and used in lieu of an autograph. This art form, which began several decades B.C., came to be called “glyptics,” and the carvings, once functional, became decorative. The Hermitage features 200 works of glyptic art and jewelry from its collection, alongside modern jewelry provided by the TENZO jewelry house, founded by Alexander Tenzo in St. Petersburg. —J.V.