This question already has an answer here:
In The Tavern we report and flag spam on the network, and it seems that some of the spam that still passes through the quality filter, has only a URL as title, nothing else. I believe posts like this can be blocked by SE's filter: I've never seen a legitimate post with only a URL in the title (and I also cannot imagine one). Titles that contain a URL can certainly be valid if they have some more title content, but not if there's only a URL.
Can posts with URL-only titles please be blocked? That could reduce the amount of spam posts a bit.