There are 2 types of sigils: the major sigil and the minor sigil.
A major sigil, also known as vitals, is a weak point on a colossus that is used to hurt and kill it. A colossus may have more than one major sigil on its body and each one must be damaged - by any means - and finally pierced with a sword to slay the colossus. Therefore, a colossus cannot be killed by using only non-sword weapons (e.g. Flash Arrows, Harpoon of Thunder). After a stab, a sigil may disappear, indicating that the colossus is no longer sensitive in that area and that the player must target another one.
When a major sigil is stabbed or shot, the wound sprays a black ichor that creates a dark cloud around the weak spot. The colossus will also react to a damaged sigil in a many - often aggresive - ways. They will scream, bellow, shriek, cry, roar, howl (and more) when stabbed and often try to shake Wander off their body.
The major sigil's pattern also appears on the front and back of Wander's garb, on Mono's dress, and again on the front and back of Lord Emon's cloak. Also, the major sigils are meant to contain the essences of Dormin within the colossi. From this we can conclude that the society, from where Wander and Emon have traveled, know about the nature of the magic that allows Dormin to be kept imprisoned.
A minor sigil, also referred to as a wound, is a weak point on a colossus that inflicts very little damage to the colossus when struck, but is often necessary to reach one or more major sigils. There are 2 regular ways to trigger a minor sigil: either stab it with your sword or hit it by shooting at it with arrows. It is, however, possible to trigger minor sigils with Flash Arrows and the Harpoon of Thunder, but it requires genuine skill or a lot of luck. Minor sigils do not appear on every colossus, but only on a small selection. The colossi with minor sigils and their respective locations are:
|Colossus||Amount||Location||Weapon of choice|
|Valus||1||Back of its left leg||Sword|
|Phaedra||1||On its neck||Sword|
|Hydrus||3||Behind each spine||Sword|
|Argus||1||Back of its right arm||
Lower back, Upper left arm