This logo is a rotational ambigram. Meaning you can rotate it 180 degrees and read another or the same text. For more info on ambigrams in logo design please check the ambigram design case.
This logo was on the cover of Dan Brown's book 'Angels & Demons'. As a result of Dan Brown incorporating ambigrams into the plot of this book and his other bestseller the 'Da Vinci Code' ambigrams become very popular. John Langdon designed several ambigrams that were used on the book covers. A an homage to Langdon, Brown named the hero in his novels Robert Langdon.