In medieval times, knights in full armor painted their coat-of-arms on their shields to identify themselves to both friends and opponents. Nearly every family had their own coat-of-arms, and when two different families intermarried, the coats-of-arms were often combined. People had their own individual coats-of-arms as well. You can imagine that the heralds, who designed and recorded these many symbols, were kept quite busy.
In Redwall, there is less need for coats-of-arms. Full armor is rarely used. It's useful, however, for flags - I believe various forts and castles in Redwall probably have their own banners and flags and coats-of-arms as well. However, I'd expect that the symbols used on the Redwall coats-of-arms would be fairly different than the ones in our medieval world. If you want to design a Redwallian coat-of-arms, you'll have to use your imagination.
The medieval heralds didn't have colored ink, so they had to draw different designs to show what color went where when they were designing coats-of-arms. The actual shields were colored, of course. Each color, or tincture, had a meaning as well. Tinctures were usually called by their Latin names when referred to in heraldry.
The following information is just a scratching of the surface of heraldry. For further information on medieval heraldry, you'll have to visit one of the heraldic sites in the Armory links.
Silver and gold tinctures were called "metals," even though they were really yellow and white. I suppose silver and gold just sounded more regal to the heralds.
Gold, commonly called Or in heraldry. It was depicted as yellow, and when drawn on paper, was drawn as dots. It stood for generosity.
Argent meant "silver," although it was really white. It was always drawn as white on paper as well, and stood for sincerity and peace.
Purple was purpure, drawn as diagonal lines, and stood for justice, sovereignty, and regality. Usually only ruling families were allowed to use purpure on their coats-of-arms.
Gules was the word for red, and it was drawn as vertical lines. It stood for warriors, martyrs, and military strength.
Blue, or azure, was drawn as horizontal lines. It symbolized strength and loyalty.
Vert meant green, drawn as diagonal lines. Green stood for hope, as well as loyalty in love.
Black was named sable, and was drawn as a grid. It stood for constancy and grief.
Orange was sometimes called tawny and sometimes called tenne. It symbolized worthwhile ambition.
Sanguine meant maroon, though it was also called murray. It meant victorious or patient in battle.
Some of the colors, when mixed with another color in a pattern, were called furs. There are several, but I'll list three of the more common here.
This is ermine - sable on argent.
When the colors were reversed, ermine became ermines - argent on sable.
The same pattern with a gold background color (sable on or) was called erminois.
Ordinaries were the patterns commonly used in heraldry, but were also called shields. Like everything in heraldry, they had their own meanings. Here are some common ordinaries.
The Cross meant a Christian, one who had served in the Crusades.
The Chevron symbolized the roof of a house and signified protection and faithful service.
The Pale symbolized military strength and fortitude.
This is the Chief, which represented dominion, authority, wisdom, and achievement in battle.