Comment by kotaKat

The nice thing on iOS at least is that they make it known it's a flash message. You'll get a full screen modal dialogue including a "Why did I get this message?" link that informs you about it and also informs you that sometimes they're used for scams.

https://i.imgur.com/lrSrm0n.jpeg

Android just gives you a generic popup that says "Class 0 message" in my testing.