Ambigram types include inversions, mirror images, chains (linked to infinite repetitions of the word), and symbiotgrams (composed of two words, one viewed from one vantage point and the other from a second). The logo depicted here, for the Latin American radio network EXA FM, is an inversion ambigram: it reads identically when rotated 180 degrees. (The design blog Brand New, in comparing this logo to its predecessor, declared the redesign "exa-llent.")
Ambigrams are "the hottest trend in typography since Helvetica," Wired magazine said in its April 2009 puzzle issue. Read the article to see 11 examples of unusually clever or cryptic ambigrams. And check out the work of artist and graphic designer John Langdon, who created the ambigrams seen in Angels & Demons and The DaVinci Code. Langdon and Scott Kim, whose work is featured in the Wired article, independently rediscovered ambigrams about 35 years ago. The first ambigrams, by children's book author Peter Newell, were published in a 1893 book, Topsys & Turvys.