Watch List notes:

ABBASID: 'Ubayd Allah, 788-790, AR dirham (2.87g), Arminiya, AH172, A-219G, Vardanyan-32, with the reverse legend mimma amara bihi al-amir / 'ubayd Allah bin / amir al-mu'minin and no other names or titles, bold VF, RR. There is no clear evidence that 'Ubayd Allah (b. al-Mahdi) ever claimed to be heir-apparent to the caliphate, as inscribed on this coin.

Estimate: 400-500 USD