Thought I'd compile a short list of resources for the invention of heraldry and coats-of-arms. Many characters are from noble families, or have fought on behalf of a state or organization which would have its own heraldic device, so knowing the standards of heraldry and blazons may come in handy as a player.
The first links are obvious, to Wikipedia's articles on Heraldry and Blazon. Blazon is the (mostly) standardized method of describing a heraldic symbol so that someone else can reproduce it. The blazon is a very specific formula with its own syntax that specifies colors, divisions, emblems, and arrangements of the heraldic emblem. With blazon terminology, one can describe a shield or coat-of-arms more accurately and with fewer words than with regular English.
This page is from a gaming miniatures decoration website, and extremely good for visualizing what the blazon terminology means in graphical form. The Canadian Heraldic Authority is also a good resource, with a fun little pdf for kids on the subject that is actually quite good at describing how heraldry is inherited and modified in the inheritance.
If anyone else has any other info to share about heraldry, please add it in the comments.