If you don't know what it means, you play the album backwards, and there is something being said.. or a meaning.. how ever you want to consider it it...

Found the most blatant thing I've ever heard yet...

Laurie Anderson, Big Science, Example #22... Played forward, it was gibberish.. I stopped it and played it backwards, and it was like playing forwards,.. It's in red magic marker

Anything blatant you know of?

Frank Zappa was forced to edit "Mother People", so he put the edited verse in backwards at the end of the first side of " we're Only In It For THe Money"

I'll have to keep my eyes open for that one..

'Empty Spaces' on The Wall, by Floyd, comes to mind.
I could tell you what the backwards message says, but then I'd have to kill you.:D