Perhaps a corruption of blue repeater, one of the British signal flags.
- (nautical) A blue signal flag with a white rectangle in the centre, signifying "P". When flown alone, indicates that a ship is ready to sail, requiring all crew members and passengers to return on board.
- We lay out in the stream for another whole day, with the Blue Peter flying, to show that we were ready for sea, and to summon any passengers who might yet remain on shore. — W.H.G. Kingston, "Peter the Whaler", 1851
- 1881, Robert Louis Stevenson, Virginibus Puerisque:
- If we clung as devotedly as some philosophers pretend we do to the abstract idea of life, or were half as frightened as they make out we are, for the subversive accident that ends it all, the trumpets might sound by the hour and no one would follow them into battle - the blue-peter might fly at the truck, but who would climb into a sea-going ship?