NAV marker transmitter
From Halopedia, the Halo wiki
The NAV Marker Transmitter[1][2] is a small ground tracking device of the United Nations Space Command.
They are small devices, relatively the size of a tick, and can be discreetly attached to an object and will Broadcast the location of that object to a nearby UNSC Heads-Up Display calibrated to their frequency.
NAV Marker Transmitters have been used by Spartans during operations, such as the raid on URF Jefferson Station.
