This is a vintage mold called "kashigata". Waves are a very traditional and popular design here in Japan.
Often made of sakura (cherry wood) and seasoned for about 3 years before carving, kashigata were used to make dried confectionery made of rice flour and sugar called rakugan. Earliest records show that this practice dates back to the mid-17th century. These confections were used as offerings and snacks for celebratory occasions and even unfortunate events. For example when a person died, it was expensive to give flowers or fresh food so, people made these sweets in the form of flowers, fish etc. These items were then placed on the "butsudan" (family shrine found in the house) for the dead person.
Kashigata were also used in the making of wagashi (nama-gashi or freshly made cake and hi-gashi or dried confectionery) for tea ceremonies.