Clue 1, announcing the arrival and departure of intelligence gathering ships and aircraft would have a rather serious impact on their effectiveness. Clue 2, intelligence gathering ships and aircraft are clearly marked.
In war, false flags are flown -- not too often -- but often enough and with devastating results if not countered that unless the potential combatant is positively identified -- by radio calls, for example -- you just take them out and ask questions later. Hot war does not provide the decorum and comfort of asking questions first. That politeness is deadly -- suicidal.