Come on guys and gals Roman coins with BC dates on! I would have thought it pretty obvious they were fakes.
AD dates weren't used either (certainly not until perhaps the Christian period). Roman coins are dated by the Consul date. Kind like ANNO REGNI's on English coins e.g ANNO REGNI XII (In the 12th year of the reign).
The Christian caledar was applied to this system later and of course it could be worked out because you historical records had recorded how long Emperor's had reigned for and thus you just have to find a fixed point (i.e present day) go back and work everything out by doing your sums.
Also note that Tiberius and Claudius (the two Emperors named on your coins) were both followers of the Religio Romana and not Christianity as Christianity was just starting out as a cult at this time.