Johnny-be-good

Johnny-be-good

dated slang One or more police officers or the police in general. (Though the term is gendered, it does not necessarily refer to a male officer.) The guy was trying to break into the store in broad daylight, and he was completely unfazed when Johnny-be-good rolled up to arrest him. The company's CEO was taken away by Johnny-be-good on charges of embezzlement and money laundering.
Farlex Dictionary of Idioms.

Johnny-be-good

n. a police officer. Here comes Johnny-be-good, so be good.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • John Law
  • Johnny Law
  • boys in blue
  • the boys in blue
  • women in blue
  • girls in blue
  • boys and girls in blue
  • men (and women) in blue
  • men in blue
  • be on the run