blue peter

a blue signal flag with a white square in the center, flown by a merchant ship to show it is ready to sail

Origin: prob. < blue repeater, signal flag used in Brit Navy

See blue peter in American Heritage Dictionary 4

noun
Nautical

A blue flag with a white square in the center, flown to signal that a ship is ready to sail.

Origin:

Origin: From the fact that it represents the letter P in the International Code of Symbols

link/cite print suggestion box

More from YD