System Surveillance and Reporting Transponders
I do not remember it in canon anywhere, but IMTU I have made up the following:
Since radios and other transcievers become increasingly inexpensive, the boonies (systems with C - E starports) are patrolled sparsely enough for pirates to be a problem, some mechanization is necessary to assist the patrollers. This would be a combination of active (radar satellites around gas giants), and passive repositories (usually on moons and asteroids).
Some free trader needs to transit an E system and gets jumped by a CP, eitehr at the gas giant or main world, on the way to skim or wilderness refuel. The distress message, any sensor signature, and imagery of the CP is blasted out by the active satelites to the passive repositories. The free trader, alas, is subject to the whims of the evile pie-rats. Said evile pie-rats, however, are caught on candid camera. They can certainly spot the active sensors, and take them out, but they have no way of spotting the repositories. If they know what is good for them, they run fast or hide deep, becasue the next type S or T that comes by will query the repositories by coded tight-beam, and pass the information on to the next port, which will use fleet couriers and x-boats to blast it out. One such set of telemetry is unlikely to help, but the next place the evile pie-rats go a hunting, or even in transit, they likely get sensed. The sensor signatures, times and locations go into the big IN computers. The data always goes in a strait line, often at J6, and the evile pie-rats do not. Eventually, their profiles get far enough ahead of them that targetted patrolling makes life very hot.
This is one reason why simply taking cargo and leaving the ship to limp away is often the best course. The real killers (space the crew and passengers with no commercial or entertainment value, take the cargo, strip the useful fittings from aboard, and blow up the ship) will glow brighter on the IN's network, and cause more of a reaction.
Also, a missing ship can also be spotted, and may got into the same profile. (There are two places that a J3 ship could have jumped from here; a free trader was headed to one at the time when that jump 3 ship would have been there. This increases the chance that the ship is at systems A,B or C by [insert really complex algorythm here]). A free trader can blast a report to the network, transmitting in the blind, as it were, as to where they are from and heading; it will show up on the network, eventually, if they come up missing. May not be much help for them, but it may, and it may help find their killers if they are jumped.
Of course, if the Scout Courier gets jumped before it can jump out, then the message goes slower. IMTU, this is why the LBB1 scouts had such a low survival. They got jumped a good bit in their travels. The pirates would almost ALWAYS run from the navy, but jumping a scout might mean the difference between life or death. This is why ex-IISS and pirates have feelings towards eachother somewhat more hostile than the Russians and Germans in 1945, IMTU!