One way would be like how in FPs games, the border of your screen or view briefly highlights in red to show the direction of attack.
I wouldn’t personally want it at all for AoE so I’m hesitant to mention it, especially if it hasn’t been proposee before… but I could see it being a useful option (yes, “option”) for people to enable, especially hearing-impaired players.
What happens when battles are going on all around your view, particularly in late game? Well, that might get to be a little much.