WordNet sense 1 (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):

USSS, United States Secret Service, Secret Service, US Secret Service

WordNet sense 2 (special police force in Nazi Germany founded as a personal bodyguard for Adolf Hitler in 1925; the SS administered the concentration camps):

Schutzstaffel