Debatable.
I doubt Walt built Sleeping Beauty Castle to be the symbol of Disneyland. Even the original opening title sequence to the Disneyland TV show originally used the Main Street train station, not the castle. The castle was used for the Fantasyland segments. Magic Kingdom inherited the castle because it was built in the style of Disneyland. It was a recognizable structure and became an early icon for Walt Disney World (including the Contemporary tower).
This icon business started when Epcot opened, as Disney needed to market the addition to Walt Disney World. The original passport tickets were park specific and had either Cinderella Castle or Spaceship Earth on them. The Studios furthered the notion by using the Earful Tower as an icon to add the idea that more was added to the resort. Again, marketing. The Earful Tower is probably the beginning of building a structure for the purpose of an icon. It isn't an attraction, not near the hub or front of the park, and the addition of the Mickey ears made it decidedly Disney.