Superknit Polyester Storm Warning Signal Set 4 by US Flag Store. $36.75. US Made by a Leading Flag Manufacturer. Low Cost Shipping Available!. Canvas Header and Brass Grommets. Superknit Polyester Material. Contains Two Hurricane Flags and Two Gale Pennants. Our Superknit® polyester Storm Warning Signal sets are printed polyester with canvas header and brass grommets. This set contains two 36"x36" hurricane flags and two 36"x72" gale pennants.