Whistle: Verb: (assobiar/assoviar) To produce a clear musical sound by forcing air through the teeth or through an aperture formed by pursing the lips. Noun: (assobio/assovio/apito): A small wind instrument for making whistling sounds by means of the breath. A device for making whistling sounds by means of forced air or steam: a factory whistle.

Whistler: (assobiador/apitador) One that whistles: a whistler of popular tune
Whistleblower: (fiscal/vigilante/denunciante/delator/informante) One who reveals wrongdoing within an organization to the public or to those in positions of authority: “The Pentagon's most famous whistleblower is . . . hoping to get another chance to search for government waste” (Washington Post).
Blow the whistle: (delatar/informar) (a) Expose corruption or other wrongdoing, as in The President's speech blew the whistle on the opposition's leaking information. b) Put a stop to, as in: The registry decided to blow the whistle on new vanity plates. The term originally alluded to ending an activity (such as factory work) with the blast of a whistle.
Whistleblowing: (denúncia): Whistleblowing at work : tough choices in exposing fraud, waste, and abuse on ...

Whistle Stop Tour: (Tour de Trem) a) A town or station at which a train stops only if signaled. b) A brief appearance of a political candidate in a small town, traditionally on the observation platform of a train:
Obama Kicks Off 'Whistle-Stop' Tour (OBAMA INICIA TOUR DE TREM) - Obama appealed to Americans to persevere through hard times as he kicked off a "whistle-stop" train tour from Philadelphia to Washington.
Source: Answers.com; New York Times, etc.