Be prepared for the zombie apocalypse. With this shirt other survivors can tell from a distance that you aren’t yet one of the shambling undead. Or should the unfortunate have already happened then this shirt would likely confuse a survivor into letting you get within chomping range.
And because you never know when the zombies are going to rise I would heartily suggest that you wear this shirt every day. Or buy seven, if hygiene is a thing that is important to you.