Space buoy

A space buoy or marker buoy was a navigational marker placed in a particular location in space as a aide to travelers.

Upon encountering Balok's cube in 2266, Spock suggested that it might be a marker buoy or potentially a form of "flypaper." 

The United Federation of Planets had a system of signal buoys in place. 

Buoys could also be used as sensor devices in a way similar to mobile probes. In 2370, as a security measure, the Federation established a series of checkpoints and sensor buoys along their border with Cardassian space. 

In 2370, Hekaran scientists rigged space buoys to produce verteron pulses, which ultimately disabled the USS Fleming, a Ferengi marauder, and the USS Enterprise (NCC-1701-D).