I imagine that you probably already know what an ambigram is, even if you’d never heard of them until Tom Hanks did his brisk walk-and-talk exposition at the beginning of Angels & Demons. Not that I would recommend going to see the film to find out (or, having seen it, for any other reason) — far better that you go to the horse’s mouth, as it were, and visit John Langdon’s site instead.
Or (and I mention this merely in passing) you could always go visit my ambigram site instead! I have very recently spruced up my gallery at
www.55cards.com/ambigrams, and so thought I’d give it a plug on BrettSpiel. So go visit! (If the notion of lots of upside-down typographical what-nots and gee-gaws excites you, that is.)