I have that necklace - DH and DS bought it at Mouse Gears at Epcot and I love it!! But you're right...people who don't know me don't seem to see Mickey. But everyone who does know me sees it right away.
I have the same thing with my watch - the whole band is open Mickey heads and it is fun to see who notices what it is, and who doesn't.
Hidden? Not to a Disney fan!!!