6th emission of Siscia, 279 CE.?
Perhaps struck at the same time as the aurei RIC 579?

Not listed in RIC; Pink -; Siscia. Denomination: Denarius.

OBV.: VIRTVS PROBI AVG

Helmeted, cuirassed bust right.

REV.: VIRTVS PROBI AVG

Emperor in quadriga right, holding sceptre, surmounted by eagle.

Mintmark: //

Weight: 2.90 g.

Image provided courtesy of Philippe Gysen