oriflamme
The red silk banner of St Denis, which the abbot of St Denis gave to French kings as they rode to war in the Middle Ages.
historical
The white banner with the golden lilies of France has been unfurled. The oriflamme has been presented to the virginal bride who stands before the altar in the forest chapel.
Any banner, idea or principle which serves as a rallying point for those involved in a struggle.
figuratively
And be your oriflamme to-day the helmet of Navarre.
Something resembling the banner of St Denis; a bright, shining object.
literary
This is that famed Martial law, with its Red Flag, its 'Drapeau Rouge:' in virtue of which Mayor Bailly, or any Mayor, has but henceforth to hang out that new Oriflamme of his; then to read or mumble something about the King's peace; and, after certain pauses, serve any undispersing Assemblage with musket-shot....
Where it comes from
From Old French oriflambe, oriflamme, from Medieval Latin auriflamma (“golden flame”), from Latin aurum (“gold”) + flamma (“flame”).
Adapted from the Wiktionary entry oriflamme (CC BY-SA 4.0).