You can tell by how they use the words.
Oh, you could look a little deeper – at their social profiles, or their blogs, or which newspapers they read – but you usually don’t need to. The words are enough. The ones they choose, and the tone that surrounds them. You can always tell.
There’s always a moment of disbelief for me. I assume I’ve misread, and I go back and try again. I begin the paragraph anew, this time more carefully, attempting to reconcile the words with my own worldview. But I fail. There’s no connection between there and here.
Mostly, it’s the adjectives that give them away. The ones they spit out in disdain.