Vintage Viking Celtic RDC "88" Penannular Brooch Cloak Pin Medieval Ren Faire

This Penannular Brooch Cloak Pin may be a rare piece. The Penannular Width and Length is 2 1/2" by 2 1/2". It's Maker's Mark says RDC 88. seal on it. The Pin Length is 2 3/4" Long. except for naming a Randy Corwin as the possible artist or jeweler.