Heralds in action!

Here, in this image from Froissart's Chronicles, you can see the Battle of the Tyne in the Anglo-Scottish War. The Scottish are on the upper left (note the gold banner with the red lion). The English are on the lower right. King Edward is seated on his horse (as evidenced by the English arms on the horse's barding). The English herald is in the upper left, climbing up to palaver with the Scots.

par la courtoisie de la Bibliotheque Nationale de France

The square banners are pretty typical of what medieval flags looked like. Note the green banner on the English side with writing on it. This was a common way for units to mark themselves in an effective yet non-heraldic manner (hint, hint).

Detail of the herald. I have no idea what that black thing is in his hand; either he's doffing his hat or about to take their picture!

This unnamed and unsung herald is engaging in one of the traditional duties of heralds: being a messenger. By wearing the tabard, the herald is speaking with the King's voice.