US Secret Service - the United States intelligence agency that protects current and former presidents and vice presidents and their immediate families and protects distinguished foreign visitors; detects and apprehends counterfeiters; suppresses forgery of government securities and documents.
It's  blessings not blessing.. The entire clause is ...to secure the  blessings of liberty to ourselves and our posterity....    The blessings of liberty refers to all of the benefits that are  afforded by having liberty.
The statue represents the Roman goddess of freedom, Libertas. Lady Liberty is holding a torch and a tablet that is inscribed with, July 4th, 1776 in roman numerals, representing American Independence Day. The statue symbolizes hope and freedom for all Americans and all who enter the United States.