There are rules in place that won't show someone's signature at all until they have made 5 or so posts, although it will let them put on in.
While this does mean that you'll sometimes briefly see a signature with links for a new user who has only been here a day who is posting a lot, this is an almost sure sign they are a spammer, so it's useful for finding them.
What I could do though, is add a one week delay so you won't see signature spam by brand new users.