Cheese It Meaning

(idiomatic, slang) An imperative used as a warning to stop, hide, or flee

Example: 1960, P. G. Wodehouse, Jeeves in the Offing, chapter VIII:
  Knowing that Bobbie would be on sentry-go made all the difference. Any gangster will tell you that the strain and anxiety of busting a safe are greatly diminished if you've a look-out man ready at any moment to say “Cheese it, the cops!”