There has been a theory that Vespasian put pigs on his coinage as a backhanded slap towards the Jewish people. The fact is that pigs or wild boars have been on coins well before Vespasian. During Roman times the pigs and respective accompanying piglets represented prosperity for the Romans. A wonderful article from Mark Markovitz in CoinWorld even tells the tale of the Romans attaching burning torches to the tails of swine and then letting them loose in battle in order to scare the elephants from the opposing army.