Ancient Rome used it on their coins, the SECVRITAS REIPVBLICAE coin Didi99 found is just one example. There are multiple others like RESTITVTOR REIPVBLICAE, SALVS REIPVBLICAE, GLORIA REIPVBLICAE etc.
If I'm not mistaken republic had somewhat of a different meaning back then but even today a lot of countries that claim to be republics and put it on their currency are far from what a republic should be.
I collect and deal in ancient Roman coin. In case you're looking for affordable ancient coins or need any help with the coins you already have send me a message.