First, don't leap to judgment that they are intentionally surveilling you. It may be hard for you to realize this, since you have a smart device to stick your nose into. But many people either don't... or have good reasons not to, such as they are standing and need to hold onto stanchions, or are retaining their situational awareness against pickpockets, gropers and the like. This can be even moreso if they are standing and you are seated.
Second, there's often nowhere else to put your eyes, which wouldn't have the same effect on somebody else. You don't want to make direct eye contact, so faces are right out. Staring at the Sikh's robes is no good either, as it makes them feel judged and unwelcome in society.
Third, just because their face is aimed your way does not mean they are looking, or processing what they see. Most people are not aiming to snoop, but they have to aim their face somewhere.
And then you have this shiny flashy thing that catches the eye, begs to be looked at, and is not direct eye contact, a minority person, a child, a crotch or breasts.
All that to say... any IPX approach you take which presumes intentional snooping is wrong out of the gate.
So the first step is to ask yourself if you're being oversensitive. Second, ask whether it's really good etiquette to use your smart device in this way in such close quarters - good question. Maybe they are staring to judge you and make you feel uncomfortable so you'll stop. It is definitely rude to let it play sounds, or to use "overloud, leaky headphones", you know the ones. Or do very flashy things, or have it much too bright for conditions, and I don't need to tell you not to view porn or radically offensive content. I realize that's intra-personal advice, so off-topic here... but it could obviate the following.
First, move, tilt or shield your screen... And do be subtle, so they do not feel like you're accusing them of snooping, which as I said is a nonstarter. If they are inadvertently staring, this will jar them out of it and they will stop.
Then dim your screen down so it's not so bright. If it's slightly hard for you to see, it'll be harder for them to see.
Then change your content - either look at things you just don't care if they snoop, like the New York Times, or something impossibly tedious to a spectator like Farmville or any of the "Quest: bring me 10 rat ears (and most rats don't have ears)” type RPG games. Or something so impossibly technical or boring-to-outsider that the snooper can't follow it, like TeX or Code Golf or whatever you're into.
Or load up serialized episodic content like Orphan Black or HPMOR that you can't possibly understand without the full backstory. If you speak a foreign language, switch to content in that.
It can be annoying to have to shake off snoopers, but first, they probably aren't, and second, it's the ultimate "first world problem" - in 1949 you would be another hat and newspaper in a trainload of hats and newspapers. Instead you have this smart device to play with, to be a victim of that makes no sense.