Again, please correct me if I'm wrong, but I was under the impression that their sources are these boards, and other boards where the rumors are discussed openly. We don't use codes when we reference them, so I don't fully get why they're doing it. If it's just to have some fun, cool! But anyone with a specific interest in this stuff is going to clock these symbols pretty easily, and it's really only people with a specific interest who are paying attention, anyway.
I get that the Twitter account reaches more people than probably all the boards and subreddits combined. Also, the maps do look somewhat "official," so maybe the company monitors them in a more aggressive capacity. But I also know that the company watches this thread, too (hey guys!), hence the very big disclaimer on the first post year after year.
So I guess I just don't see the purpose. But I digress.