Meaning of church flag in English:

church flag

noun

Nautical
  • A flag flown on board a ship to indicate a religious service is taking place.

    In the British Navy, the church flag is a white pennant with a St George's cross in the hoist and striped red over white over blue in the fly. In the United States Navy, it is a white pennant with a blue cross.

Origin

Mid 19th century; earliest use found in Sailor's Magazine.