Watch List notes:

ROMAN IMPERIAL AND PROVINCIAL COINS

Claudius, 41-54. Quadrans (Copper, 13 mm, 4.09 g, 6 h), Rome, 25 January - 3 December 41. TI CLAVDIVS CAESAR AVG Hand left, holding scales, with PNR below. Rev. PON M TR P IMP COS DES IT around S.C. RIC 85. Von Kaenel Type 64. An absolutely splendid, sharply struck coin with a fine brown patina. Good extremely fine.

Ex Gadoury, 6 December 2014, 83.
Exactly what the letters PNR mean on the obverse of this coin is debatable: they probably stand for Pondus Nummi Restitutum, 'the weight of the coinage restored'. However, this change in weight refers to Claudius' initial gold and silver coinage, and why that should be commemorated on the smallest of all aes denominations is obscure.