From a reader:
Is it permissible to recite the pledge of allegiance at Mass before
the final blessing and then omit the final blessing? Is it permissible
to display the American flag on the main altar during Mass?
Omit the final blessing? NO! Not unless there is a liturgical reason to do so.
But to have the Pledge at that point? Before the blessing? That’s out of place. After Mass would be okay. In the past I have after Mass willingly lead people in a recitation of Archbishop Carroll’s prayer for public figures. When I am in England I have after Mass happily lead a prayer for the Queen.
I believe there is no law for the universal Church that governs the placement of flags in church. Diocesan bishops could issues particular rules for their dioceses. However, if memory serves, flags in the sanctuary itself are discouraged.