From Halopedia, the Halo wiki
This weapon is the secondary weapon used by Pavium and it's mainly use to have Mega Turrets to force target a single unit or a certain unit within a group. It can also target aircraft but that won't effect Mega Turrets.
The Target Designator is only wielded by Pavium and can be used in Campaign, Multiplayer & Blitz mode.
List of appearances