There is another poster with a different picture and that makes me wonder if maybe They're coming has to do with the trains and each poster belongs to a train and it's name, especially since all of Maverick's trains are named and they're right next to each other. Just a thought.
Top 5 Steel: Steel Vengance, Maverick, Millenium Force, Kraken, Montu
Top 5 Wood: Shivering Timbers, Blue Streak, Zach's Zoomer, Mean Streak, Wolverine Wildcat
Mean Streak: Never Forget - But Steel Vengeance might've stolen my heart.