This paper analyzes the role of Israel Hiebner's Mysterium Sigillorum (1651) in the astrological reform program of late seventeenth-century English astrologers. Hiebner was a professor of astronomy and mathematics at Erfurt, and the translation of his tract into English in 1698 was considered to be a landmark event among reforming and scientific astrologers such as Henry Coley and John Gadbury. In the face of astrology's declining reputation among learned elites, Coley and Gadbury wished to cleanse their discipline of superstitious dross and illustrate it was "experimentally true" via Baconian induction as well as by incorporation of discoveries in astronomy and natural philosophy. Hiebner's insistence on accurate planetary observations in makingastrological sigils, his use of maps in Hevelius' Selenographia as guides  in stamping his medical amulets, as well as his detailed and precise lists of ascendant planetary aspects thus was appealing to these astrological reformers. This paper also analyzes the role of the Mysterium Sigillorum in the "English Sigil War," a larger debate that existed among astrological physicians and natural philosophy about the role of these medals in medical healing.