No, the compound noun 'secret service' is a common noun, a Word for any secret service of any kind, anywhere.
A proper noun is the name of a specific person, place, thing, or a title; for example:
- United States Secret Service of the US Department of Homeland Security
- Secret Intelligence Service (MI6), Foreign Section of the UK Service Bureau
- The Serviço Nacional de Informações (SNI), National Information Service of Brazil
- Al-amn al-Watani, The Egyptian Homeland Security (EHS)
- Hong Kong Police Department, Criminal Intelligence Bureau (CIB)
