-Short range weapon.
For me this is a cool idea that would imply that the AI dont know where we are magically(like now), but that they have to find us or our settlement by other means.
It would be used a bit differently by AI and players:
When used by players on AI: it would add a live compass marker to the AI marked, lasting for limited time (maybe 30 minutes). This could lead to an AI settlement for a player with patience.
When used by AI on players: it would mark the player so the AI know where the player goes for limited time (maybe 30 minutes), being able to know where ur settlement is if u go there before the spray expires. I suggest they mostly use it when ur raiding their settlement, and even more when u are carrying tokens, it would have a short range so players can't (do what i usually do when im low on health) get up to melee range and shot em while moving side to side. This way u can get the tokens having been more "stealthy" and not be followed, or get em but have the ai know where ur settlement is as u get back to it.
Related note: In this supposed scenario of the AI not knowing magically where your settlement is, the spray wouldnt be enough for the ai to know enough to be a serious opponent(maybe), so they would organice regular patrols or explorers/spies around the world to get the other settlements locations for their tribe(maybe this is already implemented).