Sentinal knots

Many colors, many shapes, many fiber choices, each one unique, and each one a bit of history. Created as an individual signature by each new Sentinel Ranger these knots reveal both the competency and the identity of the individual. They are used as identifiers, especially when moving through wilderness areas, when there is a need to know who has passed that way.
If one were to visit The Wilderness Lodge, mobile hall of the Rangers, visible upon one wall would the the boards contain the knots made by each Ranger through the history of their organization. Each knot is different, and each was the creation of a Sentinel, former or current. 
Should one be travelling in the wilderness and happen upon a bit of rope, tied into a knot and secured somewhere unobtrusive, but obviously with the intent that it be seen, you can be assured that there was a Sentinel that passed through that area. A passing Ranger would know immediately who had been there and might see additional information that would indicate why they were there, if they wanted others to follow, and what the possible situation might be.
Each Sentinel cub spends much time during their training learning about knots, but also pondering what knot they would like for their own signature. As the generations pass, it can become more and more difficult to find something unique enough to be known as theirs alone. The expectations do not change, merely because the task is harder.
While not prescriptive, most knots have certain features in common. Small, durable, and either easily made, or easily carried. For those whose knots are complex, they will take to making several to have on hand when the need to mark a trail for another occurs. Easier knots might be created as needed.
Rangers working in small teams may each leave a knot when necessary, to help reveal the composition of their party. Because these knots are unique, another Ranger seeing this evidence will know immediately who is leaving the message, what skills they possess, what resources they carry, or can use, and what their likely purpose is in being in that location.
A knot with a bit of blood deliberately dropped upon it indicates proceed with caution as danger exists ahead. A twig wedged into the knot may reveal that this is a rescue mission. Only the sentinels know with clarity the meanings each bit of information contains.

Significance

A means of identifying and remembering individual Sentinel Rangers

Item type

Clothing / Accessory

Rarity

Rare in the sense that there are only a few knots to be found. The materials are common, but their purpose requires few examples.

Raw materials & Components

Generally made from some type of rope or twine, there is usually no significance to the choice of fiber used, other than availability or the preference of the individual Sentinal.