nice coin and definitely a challenge especially without any clues....ABC 2685 Tasciovanus Star has the exact geometric design with the Bull facing right on the reverse..He was the Father of Cunobelinus and this design is also found on ABC 2679 and 2682 which are other Tasc coins and he was perhaps the most prolific producer of coin designs and remains largely a mystery of history...Sego came after him and of course your coin is attributed to Sego..who came before Cunobelinus. It is speculation about who Sego was but he appears to be a ruler of the Cantiaci or Cantii...in Kent but its all theory....this info was taken from the ABC book