This shirt is particularly relevant to me, because I remember the first Satanic Panic, which was focused on backwards messages in rock music in the late seventies. (The second Satanic Panic focused on D&D, also rippled through my life in the early eighties.)
If you have a moment, click on that picture to embiggen (at Threadless) the image on this T-shirt. I think it's brilliant.
Disclosure: If you buy anything at Threadless through that link, I get shiny gold rocks which can be traded for their T-shirts.