Here are a few from MK/MK area…
There’s a tribute window with Walt’s name that faces the castle, at the top of The Plaza restaurant. I remember reading years ago that this was so he could see it from the castle. We know he never got to see WDW completed and I don’t know if this story is true. But the window is there and I love the thought, so it’s true for me. lol.
In Liberty Square, the dark portions of the walkway are symbolic of the open sewage systems of colonial times. Also in Liberty Square, look up at the windows as you walk by and think of Paul Revere…”One if by land, two if by sea.” And of course, the thirteen lanterns in the tree are symbolic of the original thirteen colonies.
I know this technically isn’t in the parks, but if you make it over to Boulder Ridge Villas at the WL (there’s a boat that will bring you there from the MK) my favorite hidden Mickey lives in one of the wooden beams in the lobby area. There’s also a good one high up on the fireplace in the lobby of the WL, fyi. Also at Boulder Ridge, is one of the trains that Walt had in his backyard. He loved trains and was the conductor of this one, as kids could ride on it.