First things: it's an AE18mm 2g with the general appearance of a fouree denarius. But not so fast. While the obverse is in fact the usual representation of the emperor with the SEVERVS PIVS AVG legend starting from ca. 201, the reverse is something completely different: Hercules club with legend PR - IM DE - CE S - C flanking the club, all inside wreath. The design is reminiscent of the Commodus issues with his effigy wearing the Lion of Nemea and is not recorded in RIC IV (almost, I'll expand on this below) at all. But what is more interesting is the presence of the mark of the Senate. If this was meant to be a 'limes falsum' after a decennalian issue of a denarius in 202, then the SC is rather anachronistic: the silver and gold coinage was imperial rather than senatorial. There is also no denarius known with these specifications and this design. So this is a very enigmatic issue, and is now known for both Severus and Caracalla, of which know with some degree of certainty that it was occasioned by the celebration of Severus decennalia (started in 202) at Rome. The SC indicates a copper denomination to begin with -- possibly a celebratory 'quadrans' used for the donatives in Rome.At least this is the easiest explanation. There are very few specimens known: 3 for Severus (including this one, see here and here for the other 2), all in copper and 2 for Caracalla (the one in RIC IV p. 279 footnote and see here for another, which looks like a fourree denarius, a "limes falsa" -- bringing us back to the possibility noted above). The CNG specimen for Caracalla -- as it could well be a silver-washed copper necessity issue "limes falsa" -- leads me to a theory that involves these 'Notgeld' issues present in large quantities to the middle of the 3rd century on the Rhine and Danube frontier. They are often imitating rare and very rare issues of the period, sometimes pairing unlikely combinations of dies, to the point of inventing types and denominations -- I have noted such a 'quinarius' and a radiate 'antoninianus' cast for Severus Alexander (both denominations are not attested in official silver module) for instance. If not for the SC marking, this spec would fit nicely in this category of necessity coinage -- although being a semi-official issue the presence of the SC could be explained in the general conditions of these very rare types being favored by the local minting 'authority' and possibly hinting to a date of issue some time after the reigns of the emperors represented, as to avoid any possible accusations of forgery and thus an infringement of the imperial prerogative on precious metal minting. Certainly, this could be a special issue quadrans for the celebrations in 202, for both Severus and Caracalla, and I think this is the direction followed by everyone from RIC IV authors to the old works by Cohen and Mionnet, who are cited in RIC p. 279 footnote. Anyone has seen this before, perhaps collectors and numismatists focused on the Severan period?