Military operations get code names, too, and random selection has its downsides. When a blitz on Iraqi weapons sites was randomly given the name “Operation Bolton” by the British Ministry of Defense, the name divided residents of the town of Bolton. “Bolton is not an aggressive town,” one resident told The Independent.

The Pentagon’s high-profile military operations are more brand name than code name: Enduring Freedom, Desert Storm, Iraqi Freedom, New Dawn.

Perhaps the most famous coded F.B.I. operation was Abscam, the late-1970s operation in which agents posed as Arab sheikhs working for a company called Abdul Enterprises and tried to bribe lawmakers. If it is not obvious, that code name was not chosen at random.

Agents and analysts typically try to pick something clever, but being too cute can cause headaches. The investigation into Hillary Clinton’s use of a private email server was labeled Midyear Exam (often shortened inside the F.B.I. to Midyear). Agents may have thought they were being tested, facing a politically charged investigation in a presidential campaign. But last year, Senator Charles E. Grassley, Republican of Iowa, questioned the F.B.I. director at the time, James B. Comey, about whether to read anything into the name.

GRASSLEY: Was the Clinton investigation named Operation Midyear because it needed to be finished before the Democratic National Convention? If so, why the artificial deadline? If not, why was that the name? COMEY: Certainly not because it had to be finished by a particular date. There's an art and a science to how we come up with code names for cases. They assure me it’s done randomly. Sometimes I see ones that make me smile and so I'm not sure. But I can assure you that — it was called Midyear Exam, was the name of the case — I can assure you the name was not selected for any nefarious purpose or because of any timing on the investigation.

Are there standard naming conventions?

Not if past practice is any indication. Some agents seem to favor odd or obscure references. Take the federal gun case Tin Panda, for example. Others reach for the obvious, like the mortgage fraud investigation named Malicious Mortgage. Cyberinvestigators often nod at industry jargon (E-Con or Fastlink). Agents have chosen names that are descriptive (Disarray), misspelled (Lemon-Aid) and iterative (Cross Country XI).