Mark

Marking is an effect caused by the Ink Mine, Point Sensor, Angle Shooter, Echolocator, and Wave Breaker. It allows the player who marked an opponent and their teammates to see the location of the marked player, even through walls. The duration of these items could be reduced by Cold-Blooded.

Appearance
It creates a transparent squid shape that wraps around an opponent, with a line leading to each member of the team that marked them, though each member only sees the line that leads to them.

Similar abilities
There is a similar effect caused by the Haunt and Thermal Ink main abilities, where the bearer can see an enemy's silhouette through walls, after the enemy splatted them (for Haunt) or was hit by ink from their main weapon (for Thermal Ink).

Also, Flooders and Grillers locate the player with a red laser that locks on to them. Grillers can track the player anywhere, but Flooders require the player to be within their line of sight.