The sign of the Holy Cross was also mocked.
"Ordo Iuris f**k off!" was the message written on the banner. Ordo Iuris being a congregation of Catholic Polish advocates.
The perpetrators could face up to five years in jail.
It is not the first time that this church is facing acts of vandalism.
The plaque at the memorial for the victims and resistance fighters from the rank of the ÖCV was smeared with anarchist symbols.
Along with France and Germany, Italy witnesses a rising number of anti-Christian vandalism led by anarchist movements.
The situation of Christianity in France has become more and more alarming in the last decade.
The lockdown imposed on the French population doesn't seem to discourage church vandals in times of the COVID-19 pandemic.