This is the patriarchal cross, a symbol for the Roman Catholic
Church. It can, as here, appear in the form of a threefoil
cross ( is a symbol for the Holy Trinity). It can also
have other forms.
In heraldry the patriarchal cross looks different. The arms are of the same or almost the same length, and it resembles the heraldic version of the cross of Lorraine. See in Group 28.