Quintillus, Rome mint, officina 6, 270 AD.,
Æ-Antoninianus (17-19 mm / 2,05 g),
Obv.: [IM]P C M AVR CL [QVINT]ILLVS AVG , radiate and draped bust of Quintillus right.
Rev.: PROVIDE[NT AV]G / "S" , Providentia standing left, officina letter "S" = digamma in right field, holding baton over a globe at foot left, leaning on scepter right.
RIC V, I, 242, 29 ; Hunter 16 ; Coh. 61 .
The digamma was the 6th letter of the archaic Greek alphabet representing our sound "w", and named "wau". In antiquity the digamma was taking on a cursive form, which came to look something like a square C with a little tail.
A typically small flan as for most Quintillus issues.