Of these, the traffic report would probably end up being the only indication, and a single pilot could easily UM a system. Imagine if seeing a single Krait MkII in the traffic report was the only sign that your system was UM'd! Lol. Which honestly, may well have been.I'm fully aware of the differences- however one important job in Powerplay is being vigilant each week and checking all data not just the obvious reports. Ship patterns, bounties, unusual movements, the lot. For core systems this is not easy, but for backwaters you can tell unusual activity.
The problem again with the bounty board is that all of this can happen while folks are asleep or at work, and the cleared by the time anyone has a chance to check. Additionally, you can easily hide activity by purposefully having 5 CMDRs rack up 10-20 mill bounties against a power, have them never pay it off, and then do your UM attack months later while clearing your own bounties regularly to stay under the radar.