Whether it's true or not, it's a recruitment poster for al-Qaeda.

It's a "Heads up, we're still out here and doing damage" announcement.

Why would the Ba'athists want to do this? They're already on the most-wanted list anyway, and this won't change it. It would make them look like chickens, and ineffective chickens at that. It might divert American investigators a little, but not much.

If it were a red herring, well, I can only think of one group who really really really wants to prove al-Qaeda is operating in Iraq. I don't think you want to suggest that any Anglo-American intelligence group would plant evidence... do you? ;)