RIC doesn’t list any siliqua with this mintmark for Theodosius I, but it is listed for other rulers—Valens, Gratian and Valentinian II. It was probably struck circa 383, which was close to his quinquennale and around the last time this mintmark was most likely used. Theodosius I A.D. 379- 383 AR Siliqua 17mm 1.9g D N THEODO-SIVS P F AVG; pearl diademed, draped and cuirassed bust right. VOT V MVLT X surrounded by laurel wreath. In ex. T Chi-Rho E RIC IX Thessalonica --
What a fantastic rarity you have right here! I had never seen the rho in the mintmark. And how cool is it that yours is not even listed!?!? Though, my lone Siliqua lacks the chi-rho, it is still a holy coin: