4 of 4Image
This one's real.
Oddly, in this example, Facebook uses buttons to provide navigation to comments on items you've posted. In the previous example, you'll recall they used a long, complex URL.
How do you know whether that button goes to a safe place?Without inspecting it more closely, there's no way to tell.
This one's a fake, but it looks real enough.
The message offers three separate ways to navigate to its target. A Sign In button that matches the Facebook style, a text link next to the envelope icon, and a long URL at the bottom of the page.
Every one of these elements should look familar to a Facebook user. Without caerful inspection, it's very difficult to tell that this one isn't legit.