Indeed struck by
Caligula, and the
obv. shows a statue of
Caligula,
his facial features sometimes clearly recognizable, with a
legend recording that the statue
had been erected "With the Approval of the Senate, the
Equestrian Order, and the
Roman People".
Why coupled with a
rev. of
Divus Augustus? The best explanation I can think of, my own new and unpublished idea, is that the statue in question
had been set up IN THE TEMPLE OF
DIVUS AUGUSTUS, which
Caligula himself dedicated in August 37 AD.
S C was normally placed on the
rev. of
Roman bronze coins, so I think its placement left and right of the
portrait of
Augustus on this coin can only mean that this
side was the
reverse. There would have been
plenty of room to add those letters on the Statue
side of the coin, if that were the
reverse; one cannot argue that the letters
had exceptionally been "forced" onto the
obverse, because there was simply no space available to place them on the
reverse as usual.
Looking at the coin again, I now see one plausible reason why S C might exceptionally have been placed on the
obverse: it might have seemed confusing if the same
reverse type showed a statue erected with the Senate's approval, a
legend expressing the Senate's approval of that statue, and letters meaning "By Decree of the Senate" with reference to the coin's production or the establishment of the new bronze coinage by the Senate under
Augustus. For the same reason, to avoid reference to two different decrees of the Senate on the
rev. of the same coin, S C was entirely omitted from Corona Civica
sestertii of
Caligula and
Claudius, with
rev. legend SPQR P P
OB CIVES SERVATOS or
EX S C (P P)
OB CIVES SERVATOS, and from Caligula's
Carpentum sestertius for
his mother, with
rev. legend SPQR MEMORIAE AGRIPPINAE. Of course the same
choice, total omission of S C, could have been made for the CONSENSV
dupondii too, so doesn't the addition of S C to the
Divus Augustus side indicate that that was indeed the
reverse? I don't think we can say for certain.