It mustn't be a cockade - remember the War of Roses - to show your intention or loyalty. A common sign was especially needed in the times before the use of uniforms.
You could use a battle cry - "Montjoye et St Denis" with the French -, or a song - "Au jardin de mon pére" at Malplaquet - to identify own troops in the powder smog of battle, a plant at hand - roses, v.s. -, ribbons around an arm - black red gold with the German Federation in 19th century -, or a ribbon sewn up to a cockade. Mostly white was used as opposed to every other colour, e.g. in the French and Bolshevik revolutions against the revolutionary red.

Wilfried