Watch List notes:

Claudius. A.D. 41-54. Æ as (27 mm, 6.49 g, 6 h). Rome mint, Struck A.D. 41-42. TI CLAVDIVS CAESAR AVG P M TR P IMP, bare head left; c/m: BON (bonum, good) within rectangular incuse / S C across field, Minerva standing right, holding spear and shield. RIC 100; BMC 150; Pangerl 42. Fine, green and tan patina. Clear countermark. 

Kraay (Essays Mattingly) believed that this countermark may have been applied under either Nerva or Trajan as it was often applied to already well circulated coins of Claudius.