Screen edge indicator
Also said as Off-screen indicator, Damage direction indicator, Threat arrow
A mark at the edge of the screen pointing to something important that is off it, such as who just shot you or where your teammate is.
The camera can only show so much, and players blame the game for being hit from somewhere they couldn't see. An arrow at the edge is a very cheap way to tell them.
Say it
“When something off screen fires at the player, show a red arrow on that side for a second, and make it twice the size if the shot is about to land.”
Where you’ve seen it
Call of Duty marks incoming fire with a red marker that shows the direction the shots came from, together with blood on the screen.
Not to be confused with waypoint
A waypoint is about where you're going. An edge indicator is about what you can't currently see, and it is often about what's coming for you.