I feel like there is no clear icon at DHS, in part because there is no clear theme or direction for DHS. The other three parks benefit from a large structure that is easy to identify even from far away or just as a silhouette.
ToT is used at DHS because it's tall, and arguably easy to identify but that one structure/ride doesn't really encompass what the park is or wants to be. Using it as "the icon" kind of feels like using Everest for an icon at Animal Kingdom. The theatre feels like a better icon to me thematically, and it's located centrally as an anchor point in the park, but it's architecturally complex and I don't know that if you made a cut out and stuck it on a shirt that the casual visitor would identify what or where it is. A park icon needs to be more than a visual landmark. It needs to be THE thing that is synonymous with that park.