Explanation: While Romans are sometimes portrayed, especially by Romaboos like myself, as a very rational, practical culture, they were also an immensely superstitious culture, like most pre-modern societies. It leads to some interesting contrasts - you can read extremely rational Roman writers like Pliny the Elder dismissing magic as poppycock, and in the next breath advocating very wearing a hyena's anus on your forearm to enchant women to fall in love with you (it's not superstition it's SCIENCE).
Featured here is the fascinus, a common all-purpose Roman charm taking the form of a... well, an erect penis. This had three functions:
First and foremost, it was a fertility symbol, and thus believed to bring good health and good luck. For that reason, you see it plastered everywhere.
Secondly, it was considered a ward against the evil eye and other curses.
And thirdly, because Romans, like we do in the modern day, found dicks hilarious, and would give them legs, wings, or depict them fighting with their owners, in addition to scribbling them everywhere.
... some things never change.