The mintmark is on the reverse in the exergue; which is the bottom bit under the line. Your mintmark is SMTSE which translates as-- "SM" sacred money "TS" from the mint of Thessalonica (TS is Thessalonica...the rest is implied) and the last letter is the workshop; There were five workshops active at the time in Thessalonica-- A, B, gamma, delta, epsilon. Below is an example that shows the reverse legend pretty clearly.
