Shortly after you obtain the ability to use Sigils to destroy the mushroom brambles, you will come across an obstacle where you must cross the river but it is blocked by brambles on the other side. There are items in the river and the game will give you the following tooltip.
“Place Sigils on rover objects and brambles. They are larger and brighter when connected.”
To solve this puzzle, you will need to shoot multiple sigil arrows so that the pink circle that appears when they are shot get connected together. As the tooltip says, they will appear brighter when they are linked or connected together.
Shoot one arrow so it is within range to burn the brambles when it is detonated. Then you need to carefully place the other two arrows (you can only have three active at once), along the items sticking out of the river so that you can reach one of the sigils with your chaos blades. This will cause a sort of daisy chain effect that will make all of them detonate in a row, clearing away the brambles and allowing you to get across the river.