This Roman silver coin came in from Mike Ruczynski, who asked for a full ID and a valuation. It’s not in good condition but I managed to pin it down.
Firstly, the coin is a silver antoninianus of Trajan Decius, who reigned from September 249 to July of 251. On the obverse is the radiate bust of the emperor and a legend that reads IMP C M Q TRAIANVS DECIVS AVG. On the reverse two figures holding a standard face away from each other; the legend on this side reads PANNONIAE.
In volume III of David Sear’s Roman Coins and Their Values an antoninianus similar to the one featured here is listed as number 9378. The type was struck at Rome in AD 259-51.
The obverse would grade about Fine but the reverse is only poor. It isn’t a scarce coin and in its present condition I would price it no higher than £4 – £5.