2 Samuel 15:10

But Absalom, having gained the hearts of the people by the methods described above, sent spies, emissaries, through out all the tribes of Israel, saying, As soon as ye hear the sound of the trumpet, then ye shall say, Absalom reigneth in Hebron. The sound of the trumpet was to be a signal to all those who favored him to proclaim him as king over the entire nation.