Is it true that some sites have site-specific hats? If so, I believe these may all be secret ones. For example, there is a rumor of tinfoil hats available over at Area 51, but this is not confirmed yet.
Here are a few secret hats (circled) that turned up at MSO:
But I have no idea of the circled ones are general or site-specific.
Do we have any secret hats of our own at ELU?