If you make your way through iFixit’s Retina MacBook 2016 teardown, you’ll see some tamper evident screws holding the hinge to the aluminum body.

Tamper evident screws are treated with a compound, after assembly, that makes it obvious if anyone applies force to the screw.

Why do this?

From this ZDNet post:

My best guess is that these fasteners take a fair load from the hinge, but at the same time are only screwed down into soft aluminum. That leads me to believe that they need to be tightened down – or more accurately, torqued down – with a specific force that’s enough to hold them in place but not enough to strip the threads. As such, if a third-party messes with them, and the hinge later becomes loose because the threads have stripped because of improper torquing (which I’ve come across a lot over the years), Apple will know about it.

Interesting.

Update: A little birdie told me that the compound is Loctite, not an attempt to detect user tampering.