In the early days of Hollywood they needed a lot of huge lights to get any kind of image on film, but the lights were a big fire hazard (MGM had a huge fire during the making of the Wizard of Oz in the 1930's that destroyed many of the sets). So because of the constant threat of fires, water towers were placed at the center of each studio lot, in case of fires on the sound stages they could use the water to quickly extinguish them, and since they were so protonate in the center of the lot, the studios would put their names/logos on the water towers.
But water towers are pretty much "the icon" of a movie studio in the 1930's, "golden age" of Hollywood, and it's really kind of dumb that they don't use the Earful Tower as the icon for the park