Since about 200 BC the Roman coins always bore a monogram. It denoted a mint official, most likely the moneyer under whose custody a certain coin series was issued. In this way Rome safeguarded a constant quality of its money, because every discrepancy from the statutory norm could immediately be linked to the liable moneyer.
The reverse of this denarius shows the initials P. Mae. for Publius Maenius, who was in charge for parts of the Roman coinage in the years from 194 to 190 BC.