Actually... "must" is pretty clear, the insignia / identifiers are not optional.

However, Korrigan, you could just use failry simple flags somehow. Most real-world flags are very simple and abstract. However, you'll want to read up on the basics of heraldry / flag design first, as not all colors are used in maps and there are certain standard shapes and layouts. (Your world may have different rules, but it's still a good idea to get familiar with the basics if you don't know them already.) Wikipedia should have all the information needed.