A kind of flags were designed for naval battles at some stage in the Civil War; those included distinguishing marks for ships

https://travismqdt216.zenbloomer.com/posts/the-legacy-of-civil-war-flags-symbolism-and-design-throughout-history

A type of flags had been designed for naval battles in the course of the Civil War; these integrated distinguishing marks for ships engaged in strive against on rivers and seas alike.