Signal flags are used to communicate messages to and from ships. These outdoor flags are crafted from durable nylon material, with extra stitching for long-life usage in marine environments. Individual Size 0letters (12" x 15") with header and grommet are stock items. All other sizes, and pennants made with rope and toggle, are made to order itemsand take 2-3 weeks for delivery. The nautical code letter U(Uniform) flag by itself indicates"You are running into danger."