How to tell if a spammer is coming?

[Solidus]

Firstly, note the signature. All lower-case and linking to a random junk site.
Then, look at the posts. These new-gen bots take keywords from thread titles and state facts about those words. It's easy to see.

I suggest using the Minimum Posts Suite plugin from MyBBcentral, use it to disallow signatures until a user has 5 posts.