Yellow Lines are currently used to show who is looking at who.
Might I suggest making this an eyeball icon. If not enough room on the left, place it on the right, or within the dark blue boundary box on the right where there is empty space, in the same space the “Notes” icon appears when hovering.
I vote for keeping the line and maybe put something in the noob onboarding about it. An eyeball icon is going to be annoyingly small on a small screen, and we have a lot of mobile users.
Hmm, maybe move that icon to the right of the character’s name? just so that it doesn’t get cluttered with the character portrait, as I could see a heavily yellow icon blending in and making the eye basically the same as the current line.