Secret Intelligence Service
The British government's external intelligence agency, responsible for gathering, analysing and disseminating secret intelligence, popping it all on a CD ROM and then leaving it on a laptop in a Ford Mondeo in Warrington. There may be a clue in the service title.
The inconspicuous HQ of MI6
The SIS is based at a major London location at the highly anonymous and hard-to-spot Vauxhall Cross building, designed by Terry Farrell. No-one would ever spot it was there, unless they looked at the signs at Vauxhall train station pointing to "MI6 Headquarters".