In addition to the post below on medieval heraldry, I have also collected numerous examples of “heraldry” before it came into existence. For your pleasure:
• Herodotus, The Histories, book I: “The Greeks are indebted to [the Carians] for three inventions: fitting crests on helmets, painting devices on shields, and making shields with handles.”
• Numbers 2:1-2: “The Lord said to Moses and Aaron: ‘The Israelites are to camp around the tent of meeting some distance from it, each of them under their standard and holding the banners of their family.'”
• Vegetius, De Re Militari, II:18: “To prevent soldiers straying from their comrades at any time in the confusion of battle, they painted different signs for different cohorts on their shields, digmata, as they call them themselves, and it is customary to do this even now. Also the name of each soldier was inscribed in letters on the face of his shield, with a note of which cohort or century he was from.”
• Tacitus, Germania, ch. 6: “There is nothing ostentatious about [the Germans’] equipment: only their shields are picked out in the colours of their choice…. To throw away one’s shield is a supreme disgrace, and the man who has thus dishonoured himself is disbarred from attendance at sacrifice or assembly.”
• Lactantius, De Mortibus Persecutorum: “Constantine was directed in a dream to cause the heavenly sign to be delineated on the shields of his soldiers, and so to proceed to battle. He did as he had been commanded, and he marked on their shields the letter X, with a perpendicular line drawn through it and turned round thus at the top, being the cipher of Christ.”
• Beowulf (lines 331-37). Beowulf arrives at Heorot:
A high-mannered chieftain
then inquired after the ancestry of the warriors.
“From whence do you bring these embellished shields,
grey mail-shirts, masked helmets,
this stack of spears? I am spokesman here,
herald to Hrothgar; I have not seen
a body of strangers bear themselves more proudly.”
• Homer, Iliad, bk. 18. Hephaestus makes a shield for Achilles:
First of all he forged a shield that was huge and heavy,
Elaborating it about, and threw around it a shining
triple rim that glittered, and the shield strap was cast of silver.
There were five folds composing the shield itself, and upon it
he elaborated many things in his skill and craftsmanship.
(This passage is followed by 124 lines describing all those things, including the earth, the sky, the sea, the sun and moon, two cities [one celebrating a wedding feast, the other at war], a field, a vineyard, a farmyard, and a dancing floor, making it the earliest recorded blazon, and surely the longest.)