When Fayde gets illusions or if she ults, u can hear the sound of one of her stance activiting which may reveal her that she used her ult....
All her illusions goes into scythe stance.. doesn't matter if she is in shadow stance

Just stand next to her when she uses her ult and u can hear the stance activite... Or when she grabs an illusion rune u can hear it activite....
Just grab an illusion rune or just ult when ure in shadow stance