King Arthur Carousel: There are three Hidden Mickeys made of jewels on the carousel horse named Jingles. This Mickey can be found (next to Mary Poppins' umbrella) on Jingles' right hindquarter.
Note: On April 8, 2008, Jingles was rededicated in a ceremony honoring Julie Andrews' service as Ambassador for Disneyland's 50th Anniversary celebration, as well as her many contributions to Disney. The umbrella is just one of many symbols meant to honor Andrews.