Similar to our world, heraldry play an important role to distinguish noble Houses or singular character. But did the westerosi heraldry follow the same rules as ours ?
TLDR: Inspired, but not similar in all points
There are some diferences between westerosi and european heraldry, as there are lot of rules in real world that are not followed in westeros:
No particular jargon: In our world, there is a particular jargon to describe coats of arms, for colors and figures. For example, we don't say "a golden lion on red background" but "gules, a lion or". Westerosi seems to lack this specific kinds of terms
Rule of tincture: One basic rule of heraldry is the rule of tincture: metal should not be put on metal, nor colour on colour. Metal refers to gold and silver, while colors are azure(blue), gules(red), sable(black), vert(green) and purpure(purple).
Therefore, some sigils like Targaryen (gules and sable are both colors) don't follow the rules.
- Limited number of tinctures: in real world, there are only two metals and five colors, and for example, two variant of greens are both considered "vert". Therefore, some sigils like Stark's (as grey and white are both considered "argent") or Duncan's(using a color gradient) don't follow the rules.