Coats of arms
Recognizing knights by their coats of arms was tricky. Tragic as the outcome could be when knights did not carry their own shields, especially in a social milieu where the rule seemed to be the interact first and ask names later, if at all, the practice of bearing somebody else's shield remained popular. A knight might borrow the shield of a friend or help himself to the shield of a defeated foe. Lancelot was especially fond of using an anonymous or a borrowed shield. On one occasion, he saved Kay from attackers, then got up early in the morning while Kay was still asleep and took Kay's arms. Kay, riding back to Camelot with Lancelot's shield perforce, arrived unmolested, since knights had already learned better than to meddle with Lancelot; Lancelot, meanwhile, being mistaken for the unpopular Kay, took the chance to leave a trail of unhorsed opponents behind him.
For anonymity, a knight could carry a plain-colored shield [white, black, green, red, and so on], or cover his shield, or even apparently do both at once! Anonymous shields seems to have been very popular with villainous knights. Blank shields, usually white but sometimes red, and presumably any other tincture, were carried by young knights in their first year of knighthood, before they had earned the right to bear a device.
Thus, when established knights disguised themselves with blank shields of any color, they would seem to have been disguising their skill and experience as well as their identities. A knight like Lancelot would do this in order to attract more attackers and thus win greater honor; a knight like Breuse Sans Pitie would do it in order to trick potential victims into a false sense of security.
Because it was such common practice to use an anonymous or borrowed shield, knights sometimes resorted to other devices in order to identify themselves. In one tournament, the companions of the Round Table wore round leather badges so as to know each other. Guenevere finally insisted Lancelot start wearing her favor in tournaments so that his relatives would know him and not gang up on him as they had done with almost fatal result to the great knight at Winchester.