Around the beginning of the 15th c. there was a fashion particularly associated with deeds of arms to the outrance. Gentlemen who wished to undertake such a deed of arms would wear a conspicuous, distinctive and precious device. The Duke of Bourbon's Enterprise was an explicit example. Challengers who defeated the gentlemen of the enterprise could win the device. If they lost, they paid a similar stake as a ransom. A 1406 challenge and Gerard de Herbaumes' challenge c. 1414 seem to be variants of the same idea. Other devices included diamonds and gold rods.*
Think of it as wearing a gilded chip on your shoulder.
I think it's interesting and significant that none of the elaborately advertised displays of martial ferocity above seem to have resulted in an actual combat. They did, however, enhance the reputation of the gentleman undertaking the enterprise.
*Juliet Barker, The Tournament in England 1100-1400, Woodbridge,1986, pp. 157-158 citing BL MS Additional 21357 fos. 1r.,2r.,3r.