For school I had to make a Napoleon hat, which called for a cockade. What is that?

A cockade is a rosette or knot of ribbon originally used to decorate a hat. The adornment later morphed into insignia of varying colors that denoted one's military unit; support for a cause; or allegiance to a group, organization, or household. The cockade was worn on a hat, armband, lapel, or — for women — in the hair. Napoleon Bonaparte wore a tri-color (blue, red, and white) cockade on his bicorne (two-pointed) hat.

In A Tale of Two Cities, which takes place during the French Revolution, Charles Darnay is escorted, as a prisoner, by two guards:

The escort were two mounted patriots in red caps and tri-coloured cockades, armed with national muskets and sabres, who rode one on either side of him.