Here is, presumably, a easy way to get rid of most of these annoying posts.

Do not allow the following sequence of letters in the first post (i.e. do not allow links).

www
http
/
:/

I know that above is redundant. Just pick or come up with whatever works best. If the above appears in the post just not allow it and report to author in the same way the post does not have enough characters. Just say you do not allow those sequence of letters in first post.