No, the compound noun 'secret service' is a common noun, a general term for any government intelligence agency.
A proper noun is the name of a specific person, place, or thing; for example:
- United States Secret Service, Department of Homeland Security
- South African Secret Service, National Intelligence Co-ordinating Committee
- Australian Secret Intelligence Service, Department of Foreign Affairs and Trade
- "On Her Majesty's Secret Service", 1969 James Bond movie