Reading these threads, there are many people... nearly all on the Pro-PK/Anti-Combat-Log side who claim they can tell this with 100% accuracy just from their victim's behaviour. No need to know anything about the connection in advance.
Of course the groups that interdict the most people notice it the most, if you interdicted players all day you'd notice it too its not rocket science to tell the difference, its about as obvious as when somebody logs out to skip leaving the docking bay - oh look! they moved 10km exactly away from the station instantly, I wonder what happened?!?!
On the topic of mode switching they don't need to fix it by stopping people doing it, they need to fix why they do it. If they actually put a wide range of missions on the board including big ones people wouldn't have to cheese the board to get resets, I've never seen a mining mission that wants more than 4 of a resource its ridiculous what are sidewinders the only mining ship?