Molanus defends the custom of using the head of the ruler on coins is allowed, however also religious signs or saints would traditionally be struck on coins.
“Let no one criticize this very ancient custom of princes to strike their image and portrait on coins. Indeed, Our Lord sufficiently approved the principle when He concluded from the engraving of coins that one must render to Caesar what is Caesar’s.
Moreover, from the constitution of the first Christian princes, the sign of the cross was engraved on coins. Portraits of patrons, not only general but also special, are also placed on the coins. Of which I have lately noted many examples, perusing the booklet of coins published by Plantin, in the year 1575.”
“Absit vero ut quis reprehendat vetustissimum illum Principum morem, quo imagines sive effigies suas nummis inscribunt. Salvator enim noster satis approbavit huiusmodi inscriptionem quando ex ea intulit, reddenda esse Caesari quae sunt Caesaris.
Caeterum ex primorum principum Christianorum constitutione, signum crucis nummis insculpitur. Ponuntur etiam in nummis effigies patronorum, non tantum generalium, sed et specialium. De quibus multa exempla nuper annotavi, percurens libellum monetarum a plantino editum, anno 1575.”
Molanus 1996, 312.