For anyone not inclined or willing to do the research (and shame on you for so being, dammit) I shall explain.
The first time you meet Shivans, your fighter is able to detect the fact their fighters are seeking or have missile lock on you. It is also able to detect the fact one of their missiles has lost this lock. This means they must be using similiar systems to you, the Vasudans, or both. Why?
Lock-threat indicators, how do they ****ing work?
Radars are really awesome things. So are ladars or whatever doohicky they're using in FS. However there are problems. Your radar is scanning a 360 bubble around your fighter out to a very long range. This slows it down enough that providing accurate targeting information on a single object at long ranges (or even short ones) is troublesome. So you either have a special radar mode or a secondary system to focus on one target to get accurate targeting data; that's the one you have locked and you cycle through them with T.
Your missiles are being passed this data and using it to adjust their own homing systems and track the target. That's missile lock time. This may also require a special mode or another secondary system, possibly the missile's own sensors.
These modes and secondary systems are detectable to other ships. If you're in a flight of twenty closely spaced ships and a Shivan locks you from 5 kilometers away, your ship knows that you're the one actually being targeted by detecting the fact you're not being hit with the primary mode/system, but with the secondary. Your fighter can tell that enemy one is going for or has missile lock by the same means. It can tell when a missile has lost you as a target because its active homing is no longer painting your hull with whatever sensor waves it uses. (Which makes MX-series locks being known evaded kind of weird but it's what we're stuck with. Maybe they meant infrared laser homing; alternately the missile is being passed control signals and that's really the Azimuth Sector light equivalent.)
The fact your fighter can detect this before the Shivans have had their electronics gear stolen in later missions means that they have to be using similar systems to either your fighter or your (known) enemies' fighters for your fighter to even recognize their targeting, missile lock, and missile homing modes.
