The sacking of Bob Quick, The U.K.'s counter-terrorism chief, for inadvertendly displaying a classified document to photographers outside Downing Street, draws attention to the procedures used to safeguard classified information in the U.S. A U.S. Army guide to protecting such material notes that if you "personally transport classified materials by car or foot to another location, you must provide reasonable protection for the information under all foreseeable contingencies," like advance photography equipment. This means that "classified information must be double wrapped or packaged as though it were being sent by mail, kept under your constant control ... and delivered only to an authorized person." Information classified at a TOP SECRET level or above draw extra safeguards.
In the UK, the "SECRET" classification denotes information that would "seriously" damage national security, while in the U.S., "SECRET" denotes "grave" damage. . (UK TOP SECRET information, if disclosed, would produce an "EXCEPTIONALLY GRAVE" damage.) The distinctions here are lost on most people who handle classified information; one common joke is that if you don't want your classified info on the front page of the New York Times, don't stamp it "Top Secret." . Other countries take this stuff very seriously -- check out Slovenia's procedures! One other question: in the U.S., an equivalent dossier related to an imminent FBI arrests of terror suspects might not be marked with an official national security classification. It might be "Law Enforcement Sensitive" or "For Official Use Only," both categories of non-classified information which nonetheless require special handling. The penalties for disclosing FOUO and LES info aren't as harsh as for those who disclose formal classified information.