Ambigram

An ambigram is a calligraphic design that has several interpretations as written.
Etymology.
The word ambigram was coined by Douglas Hofstadter, an American scholar of cognitive science, best known as the Pulitzer Prize-winning author of the book Gödel, Escher, Bach.
Hofstadter describes an ambigram as a "calligraphic design that manages to squeeze two different readings into the selfsame set of curves."
Different ambigram artists (sometimes called "ambigramists") may create distinctive ambigrams from the same words, differing in both style and form.
History.
Although the term is recent, the existence of mirror ambigrams has been attested since at least the first millennium. They are generally palindromes stylized to be visually symmetrical.
In ancient Greek, the phrase "νιψον ανομηματα μη μοναν οψιν" ("wash the sins, not only the face"), is a palindrome found in several locations, including the site of the church Hagia Sophia, in Istanbul, Turkey. It is sometimes turned into a mirror ambigram when written in capital letters with the removal of spaces, and the stylization of the letter N (Ͷ).
The first sator square palindrome was found in the ruins of Pompeii, meaning it was created before 79 AD.
A sator square using the mirror writing for the representation of the letters S and N was carved in a stone wall in Oppède (France) between the Roman Empire and the Middle Ages
A boustrophedon is a type of bi-directional text, mostly seen in ancient manuscripts and other inscriptions. 
Every other line of writing is flipped or reversed, with reversed letters. Rather than going left-to-right as in modern European languages, or right-to-left as in Arabic and Hebrew, 
alternate lines in boustrophedon must be read in opposite directions. Also, the individual characters are reversed, or mirrored. It was a common way of writing in stone in Ancient Greece.
Mirror writing in Islamic calligraphy flourished during the early modern period, but its origins may stretch as far back as pre-Islamic mirror-image rock inscriptions in the Hejaz.
The earliest known non-natural rotational ambigram dates to 1893 by artist Peter Newell. Although better known for his children's books and illustrations for Mark Twain and Lewis Carroll, he published two books of reversible illustrations, in which the picture turns into a different image entirely when flipped upside down. The last page in his book "Topsys & Turvys" contains the phrase THE END, which, when inverted, reads PUZZLE. In "Topsys & Turvys Number 2" (1902), Newell ended with a variation on the ambigram in which THE END changes into PUZZLE 2.
In March 1904 the Dutch-American comic artist Gustave Verbeek used ambigrams in three consecutive strips of "The UpsideDowns of old man Muffaroo and little lady Lovekins". His comics were ambiguous images, made in such a way that one could read the six-panel comic, flip the book and keep reading. In "The Wonderful Cure of the Waterfall" () an indian medicine man says 'Big waters would make her very sound', while when flipped the medicine man turns into an Indian woman who says 'punos dery, eay apew poom, serlem big'. Which is explained as, 'poor deary' several foreign words that meant that she would call the 'Serlem Big'. The next comic called "At the House of the Writing Pig" (), where two ambigram word balloons are featured. The first features an angry pig trying to make the main protagonist leave by showing a sign that says; 'big boy go away, dis am home of mr h hog', up side down it reads 'Boy yew go away. We sip. Home of hog pig.'. The protagonist asks the pig if it wants a big bun, upon which it replies 'Why big buns? Am mad u!', which flips into 'In pew we sang big hym'. Finally in "The Bad Snake and the Good Wizard" () there are two more ambigrams. The first turns 'How do you do' into the name of a wizard called 'Opnohop Moy', the second features a squirrel telling the protagonist 'Yes further on' only to inform it that there are 'No serpents here' on his way back. These ambigrams are all relatively simple compared to contemporary designs, but given the constraints that Verbeek had due to the drawing and story they are impressive nevertheless. In a 2012 Swedish remake of the book, the artist Marcus Ivarsson redraws "The Bad Snake and the Good Wizard" in his own style. He removes the squirrel, but keeps the other ambigram. 'How do you do' is replaced by 'Nejnej' (Swedish for no no) and the wizard is now called 'Laulau'.
From June to September 1908, the British monthly "The Strand" published a series of ambigrams by different people in its "Curiosities" column. Of particular interest is the fact that all four of the people submitting ambigrams believed them to be a rare property of particular words. Mitchell T. Lavin, whose "chump" was published in June, wrote, "I think it is in the only word in the English language which has this peculiarity," while Clarence Williams wrote, about his "Bet" ambigram, "Possibly B is the only letter of the alphabet that will produce such an interesting anomaly."
Rotational faces as optical illusion are very old, since were produced in 1550, and maybe earlier. In this perspective, was published in 1946 for the cover of a book gathering reversible drawings by Rex Whistler.
Popularity.
In 1969, Raymond Loewy designed the rotational ambigram logo, which is still in use in 2020. The mirror ambigram DeLorean Motor Company logo was first used in 1975.
John Langdon and Scott Kim also each believed that they had invented ambigrams in the 1970s. Langdon and Kim are probably the two artists who have been most responsible for the popularization of ambigrams. John Langdon produced the first mirror image logo "Starship" in 1975. Robert Petrick, who designed the invertible "Angel" logo in 1976, was also an early influence on ambigrams.
The earliest known published reference to the term "ambigram" was by Hofstadter, who attributed the origin of the word to conversations among a small group of friends during 1983–1984. The original 1979 edition of Hofstadter's "Gödel, Escher, Bach" featured two 3-D ambigrams on the cover.
Ambigrams became more popular as a result of Dan Brown incorporating John Langdon's designs into the plot of his bestseller, "Angels & Demons", and the DVD release of the "Angels & Demons" movie contains a bonus chapter called "This is an Ambigram". Langdon also produced the ambigram that was used for some versions of the book's cover. Brown used the name Robert Langdon for the hero in his novels as an homage to John Langdon.
In music, the Grateful Dead have used ambigrams several times, including on their albums "Aoxomoxoa" and "American Beauty".
In the first series of the British show "Trick or Treat", the show's host and creator Derren Brown uses cards with rotational ambigrams. These cards can read either 'Trick' or 'Treat'.
Although the words spelled by most ambigrams are relatively short in length, one DVD cover for "The Princess Bride" movie creates a rotational ambigram out of two words: "Princess Bride," whether viewed right side up or upside down.
In 2015 iSmart's logo on one of its travel chargers went viral because the brand's name turned out to be a natural ambigram that read "+Jews!" upside down. The company noted that "...we learned a powerful lesson of what not to do when creating a logo.”
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Types.
Ambigrams are exercises in graphic design that play with optical illusions, symmetry and visual perception. Some ambigrams feature a relationship between their form and their content. Ambigrams usually fall into one of several categories:
Totem
An ambigram whose letters are stacked. May be rotational or mirrored. 
Creating ambigrams.
Handmade designs.
There are no universal guidelines for creating ambigrams, and there are different ways of approaching problems. A number of books suggest methods for creation (including "WordPlay" and "Eye Twisters").
Ambigram generators.
Computerized methods to automatically create ambigrams have been developed. Most of them function on the simplified principle of mapping a single letter to another single letter. Because of this weakness, most of them can only map a word to itself or to another word that is the same length and do not combine letters. Thus, the generated ambigrams are in general of poor quality when compared to hand made ambigrams. More sophisticated techniques employ databases of thousands of curves to create complex ambigrams. Most ambigram generators are free, while some others require payment.
Other names.
Ambigrams have also been called, among other things: