When you see a post that is clearly a spam post, you can report it here:
http://www.thescienceforum.com/Repor...ere-11711t.php
(For some reasons no-one seems to want to use that thread yet.)
Then you just need to wait for a moderator to delete the spam. You don’t need to reply to the spam post. However, if you feel you have to post a reply, make sure you do not quote or make any reference to the contents of the spam post in your reply. This would simply defeat the point of deleting the spam. The reason for deleting the spam is because nobody needs to see what nonsense has been posted by the spammer; if you quote the spam contents while replying to the post, then people would know what nonsense had been posted when they see your reply.