Couldn't Apple display a little icon in the top bar, say next to the time? Somewhere no other app can use? A little padlock for example. You would just teach people to only enter their password if the padlock is displayed.
We did that for HTTPS, although that was terribly misunderstood (means "the connection is secure between you and X", not "X is actually your bank")
You can draw whatever you want onto the screen, you can not just prevent someone from drawing a little lock icon (maybe through copyright but malware authors wouldn’t care). Think of a video game, I can choose the color of any pixel on the screen. That’s the problem
We did that for HTTPS, although that was terribly misunderstood (means "the connection is secure between you and X", not "X is actually your bank")