Watch List notes:

Antonia (mother of Claudius I) Ӕ Dupondius. Rome, circa AD 41-50. AN[TONIA] AVG[VSTA], draped bust right; c/m monogram of Vespasian / [TI CLAVDIVS] CAESAR AVG [P M TR P IM]P, Claudius standing left, veiled and togate, holding simpulum; [S-C] across fields. RIC 92 (Claudius); for countermark, cf. BMCRE I, p. xliii (under Nero). 10.12g, 27mm, 5h.

Fine.

This countermark usually only appears on coins from the mint of Lugdunum, mostly on those of Nero, linking Vespasian to the last legitimate emperor.