Imagine you are new to this mod. You start exploring, find a jump hole to a non-vanilla system and think: "Lets take a look" ... as soon as you arrive, you get blown into pieces. I bet this happened often.
Even if you played a while and get familiar with the concept of guard systems ... there are so many, you cant remember them all. You could argue that a look into the wiki might help. But for at least some systems there is no line telling about this, and for others you have to read it between the lines. Even if the wiki would be rewritten that it states the status of a system properly, it still takes time to look it up and is unhandy.
Therefore I suggest to place warning bouys ~1k above and/or below any jump hole that leds into a guard system. That bouy is owned by the (guard) faction that system belongs to, so that it shows up in the right color on the scanners. In the infocard there's a text like "WARNING You're about to enter Rho-122, a guard system that belongs to the Faction X" or even shorter without mentioning the faction. Or something like that.
Pro:
- an easy way for rookie pilots to avoid getting destroyed in guard systems (although I know there will be some that dont get the hint - you cant save them all ;))
- for experienced pilots a reminder present in the game and not somewhere outside where one has to alt-tab to
Con:
- some work for the dev team ... but not too much. The bouys are easy to place, and the infocard text would be nearly all the same.
- one Item more on the scanners if you are hostile to the guards ... in the vicinity of that holes. So it would not spam your scanners.