Dear JT,
The initials at the end of the names of some priests refer to the religious orders to which they belong. The “O.P.” at the end of my name stands for the “Order of Preachers” which is the official name for the Domincan Order. “S.J.” stands for the “Society of Jesus” which is the official name for the Jesuit Order and so on.
Diocesan priests do not belong to religious orders and therefore do not put such initials behind their names.
I suppose you can check the various initials by going to Google.
Fr. Vincent Serpa, O.P.