I guess what OP meant is a button to hide all messages/posts from users with signatures, not hiding the signatures.
Brute way, doesn't make much sense, if you believe 90% of posts from sig users are spam then with a button like this you will miss out on the 10% of genuine posts by sig users. Better use the ignore button.
You understood it right.
Imagine your email box without spam filters. It would be a nightmare.
The same way we use the "Spam" folder in our email box, we would use that function to filter all the spammy messages in the forum.