What is the purpose of the signature, anyways? Mine never looks anywhere close to the same as before, and most of the readers at the bad grocery store next to m

What is the purpose of the signature, anyways? Mine never looks anywhere close to the same as before, and most of the readers at the bad grocery store next to my apartment just select seemingly random pixels anyways when you touch it. Is this seriously a security measure? Even if it did matter, it's on the back of the card anyways, for someone to copy! Why not just get rid of it?