The first sign a conventional attack us underway is when the jamming starts. Israel should start jamming four or five times a week to fatigue the defensive crews.
Of course, it would be better if the first sign of an attack was when things started exploding...
I am convinced that is what happened at the Syrian site, and that the Syrians and North Koreans had an uninvited visitor from Missouri.The second wave of uninvited guests arrived after the first had departed.
Negative.
The first sign an attack is underway is when Israeli drones get painted by Iranian Radars....which in turn get taken out by Israeli missiles.