Copy Reads:
Invented by Leonardo Da Vinci*, the Ambigram was designed to allow words to be read both normally and upside down, giving the word a sense of infinity. A fitting tool for a brand who's essence is one of unlimited energy.
*Sounds good, but one thing important to note though; the ambigram was not invented by Da Vinci. The term ambigram was coined in the 20th century by Douglas Hofstadter as a generic word for inversions. Ambigrams were made famous in the early 70's by pioneers like Scott Kim (who Isaac Asimov called "the Escher of the alphabet) and my favourite ambigram artists John Langdon.
Here's a great one (below) Langdon recently created. It was commissioned by Dan Brown (Da Vinci Code dude) to be given as a gift to Steven Tyler. I love how it retains the essence of the original Aerosmith logo.
Dan is also a big fan of the ambigram and has used it prominently in many of his works, including in the Da Vinci Code as part of the story (which may be where the confusion in the Snickers ad comes from) and even on the cover of his book Angels & Demons:
Ambigrams have also become quite popular recently with many Tattoo artists as they make for very interesting and unique designs:
Finally, while on the topic... I dug up some ones that I had tried for fun not too long ago.