I've noticed several answers that appear to only (just!) try to stay on topic while advertising a product. For example:
Further evidence is that this user signed up 7 hours ago, and has had no action before or after these answers were posted (apart from the exact same behaviour over on SO).
What should I do with these types of posts? On the surface it often doesn't look like pure spam/advertising, but is quite obvious once you've looked at the user's other answers/surrounding behaviour.