mail flag
noun Nautical.
a flag of the International Code of Signals symbolizing the letter Y, flown alone by a ship to indicate that it is carrying mail: a square flag with red and yellow diagonal stripes.
any of various other flags indicating that a ship is carrying mail.
Words nearby mail flag
mail,
mail bomb,
mail car,
mail carrier,
mail drop,
mail flag,
mail merging,
mail order,
mail-cheeked,
mail-in,
mail-order