-Under Construction-Skulls not only protect your brain from harm, they are probably also the single most badass symbol in the world.
You know how sometimes people punch you in the head, and yet you do not die? That's because your skull is protecting your brain from people's fists. Otherwise your brain would pretty much just squash like a rotten pumpkin, and it would have a sudden adverse effect on your thinking process (and seeds would be everywhere).
Even if you did not die from it, you would probably walk around drooling and unable to tie your shoes. Obviously, you need your brain, even if it's not doing that much else. Just being able to have a dry shirt and securely tied shoes is better than nothing.
The skull is just a specialized bone which has adapted into the shape of a face with a space inside for brains to go. Coincidentally, human skulls happen to have also taken the most badass and scary shape they could.
Will something kill you if you touch it? Put a picture of a skull on it! Problem solved! Now it says "Look at this, even if you are too dumb to read, touching this thing is clearly dangerous!" Admittedly, it doesn't work that well on people who don't even know what a skull looks like (ie, children under age 3), but to be fair, a lot of those people always insist on getting themselves killed no matter what you do. We suggest sending all babies to survival camp to learn better skills, and possibly, how to stop crying all the time like a bunch of goddamn babies.